1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666
|
"""
Estimate a GEV on the Fremantle sea-levels data
===============================================
"""
# %%
# In this example, we illustrate various techniques of extreme value modeling applied
# to the annual maximum sea-levels recorded at Fremantle, near Perth, western Australia, over the period
# 1897-1989.
# Readers should refer to [coles2001]_ to get more details.
#
# We illustrate techniques to:
#
# - estimate a stationary and a non stationary GEV depending on time or on the covariates (time, SOI),
# - estimate a return level,
#
# using:
#
# - the log-likelihood function,
# - the profile log-likelihood function.
#
# We also illustrate the modelling with covariates.
#
# First, we load the Fremantle dataset of the annual maximum sea-levels. We start by looking at them
# through time. The data also contain the annual mean value of the Southern Oscillation Index (SOI),
# which is a proxy for meteorological volatility due to effects such as El Nino.
import openturns as ot
import openturns.viewer as otv
from openturns.usecases import coles
data = coles.Coles().fremantle
print(data[:5])
graph = ot.Graph(
"Annual maximum sea-levels at Fremantle", "year", "level (m)", True, ""
)
cloud = ot.Cloud(data[:, :2])
cloud.setColor("red")
graph.add(cloud)
graph.setIntegerXTick(True)
view = otv.View(graph)
# %%
# We select the sea-levels column.
sample = data[:, 1]
# %%
# **Stationary GEV modeling via the log-likelihood function**
#
# We first assume that the dependence through time is negligible, so we first model the data as
# independent observations over the observation period. We estimate the parameters of the
# GEV distribution by maximizing the log-likelihood of the data.
factory = ot.GeneralizedExtremeValueFactory()
result_LL = factory.buildMethodOfLikelihoodMaximizationEstimator(sample)
# %%
# We get the fitted GEV and its parameters :math:`(\hat{\mu}, \hat{\sigma}, \hat{\xi})`.
fitted_GEV = result_LL.getDistribution()
desc = fitted_GEV.getParameterDescription()
param = fitted_GEV.getParameter()
print(", ".join([f"{p}: {value:.3f}" for p, value in zip(desc, param)]))
# %%
# We get the asymptotic distribution of the estimator :math:`(\hat{\mu}, \hat{\sigma}, \hat{\xi})`.
# In that case, the asymptotic distribution is normal.
parameterEstimate = result_LL.getParameterDistribution()
print("Asymptotic distribution of the estimator : ")
print(parameterEstimate)
# %%
# We get the covariance matrix and the standard deviation of :math:`(\hat{\mu}, \hat{\sigma}, \hat{\xi})`.
print("Cov matrix = \n", parameterEstimate.getCovariance())
print("Standard dev = ", parameterEstimate.getStandardDeviation())
# %%
# We get the marginal confidence intervals of order 0.95.
order = 0.95
for i in range(3):
ci = parameterEstimate.getMarginal(i).computeBilateralConfidenceInterval(order)
print(desc[i] + ":", ci)
# %%
# At last, we can validate the inference result thanks the 4 usual diagnostic plots:
#
# - the probability-probability pot,
# - the quantile-quantile pot,
# - the return level plot,
# - the empirical distribution function.
validation = ot.GeneralizedExtremeValueValidation(result_LL, sample)
graph = validation.drawDiagnosticPlot()
view = otv.View(graph)
# %%
# **Stationary GEV modeling via the profile log-likelihood function**
#
# Now, we use the profile log-likehood function rather than log-likehood function to estimate the parameters of the GEV.
result_PLL = factory.buildMethodOfXiProfileLikelihoodEstimator(sample)
# %%
# The following graph allows one to get the profile log-likelihood plot.
# It also indicates the optimal value of :math:`\xi`, the maximum profile log-likelihood and
# the confidence interval for :math:`\xi` of order 0.95 (which is the default value).
order = 0.95
result_PLL.setConfidenceLevel(order)
view = otv.View(result_PLL.drawProfileLikelihoodFunction())
# %%
# We can get the numerical values of the confidence interval: it appears to be a bit smaller
# than the interval obtained with the log-likelihood function.
# Note that if the order requested is too high, the confidence interval might not be calculated because
# one of its bound is out of the definition domain of the log-likelihood function.
try:
print("Confidence interval for xi = ", result_PLL.getParameterConfidenceInterval())
except Exception as ex:
print(type(ex))
pass
# %%
# **Return level estimate from the estimated stationary GEV**
#
# We estimate the :math:`m`-block return level :math:`z_m`: it is computed as a particular quantile of the
# GEV model estimated using the log-likelihood function. We just have to use the maximum log-likelihood
# estimator built in the previous section.
#
# As the data are annual sea-levels, each block corresponds to one year: the 10-year return level
# corresponds to :math:`m=10` and the 100-year return level corresponds to :math:`m=100`.
#
# The method provides the asymptotic distribution of the estimator :math:`\hat{z}_m`
# which mean is the return-level estimate.
zm_10 = factory.buildReturnLevelEstimator(result_LL, 10.0)
return_level_10 = zm_10.getMean()
print("Maximum log-likelihood function : ")
print(f"10-year return level = {return_level_10}")
return_level_ci10 = zm_10.computeBilateralConfidenceInterval(0.95)
print(f"CI = {return_level_ci10}")
# %%
zm_100 = factory.buildReturnLevelEstimator(result_LL, 100.0)
return_level_100 = zm_100.getMean()
print(f"100-year return level = {return_level_100}")
return_level_ci100 = zm_100.computeBilateralConfidenceInterval(0.95)
print(f"CI = {return_level_ci100}")
# %%
# **Return level estimate via the profile log-likelihood function of a stationary GEV**
#
# We can estimate the :math:`m`-block return level :math:`z_m` directly from the data using the profile
# likelihood with respect to :math:`z_m`.
result_zm_10_PLL = factory.buildReturnLevelProfileLikelihoodEstimator(sample, 10.0)
zm_10_PLL = result_zm_10_PLL.getParameter()
print(f"10-year return level (profile) = {zm_10_PLL}")
# %%
# We can get the confidence interval of :math:`z_m`: once more, it appears to be a bit smaller
# than the interval obtained from the log-likelihood function.
# As for the confidence interval of :math:`\xi`, depending on the order requested, the interval might
# not be calculated.
result_zm_10_PLL.setConfidenceLevel(0.95)
try:
return_level_ci10 = result_zm_10_PLL.getParameterConfidenceInterval()
except Exception as ex:
print(type(ex))
pass
print("Maximum profile log-likelihood function : ")
print(f"CI={return_level_ci10}")
# %%
# We can also plot the profile log-likelihood function and get the confidence interval, the optimal value
# of :math:`z_m` and its confidence interval.
view = otv.View(result_zm_10_PLL.drawProfileLikelihoodFunction())
# %%
# **Non stationary GEV modeling via the log-likelihood function**
#
# If we look at the data carefully, we see that the pattern of variation has not remained constant over
# the observation period. There is an increase in the data through time.
# We want to model this dependence because a slight increase in extreme sea-levels might have
# a significant impact on the safety of coastal flood defenses.
#
# We have define the functional basis for each parameter of the GEV model. Even if we have
# the possibility to affect a time-varying model to each of the 3 parameters :math:`(\mu, \sigma, \xi)`,
# it is strongly recommended not to vary the parameter :math:`\xi` and to let it constant.
#
# For numerical reasons, it is strongly recommended to normalize all the data as follows:
#
# .. math::
#
# \tau(t) = \dfrac{t-c}{d}
#
# where:
#
# - the *CenterReduce* method where :math:`c = \dfrac{1}{n} \sum_{i=1}^n t_i` is the mean time stamps
# and :math:`d = \sqrt{\dfrac{1}{n} \sum_{i=1}^n (t_i-c)^2}` is the standard deviation of the time stamps;
# - the *MinMax* method where :math:`c = t_1` is the initial time and :math:`d = t_n-t_1` the final time;
# - the *None* method where :math:`c = 0` and :math:`d = 1`: in that case, data are not normalized.
#
# We suppose that :math:`\mu` is linear in time, and that the other parameters remain constant:
#
# .. math::
# :nowrap:
#
# \begin{align*}
# \mu(t) & = \beta_1 + \beta_2\tau(t) \\
# \sigma(t) & = \beta_3 \\
# \xi(t) & = \beta_4
# \end{align*}
#
constant = ot.SymbolicFunction(["t"], ["1.0"])
basis = ot.Basis([constant, ot.SymbolicFunction(["t"], ["t"])])
# basis for mu, sigma, xi
muIndices = [0, 1] # linear
sigmaIndices = [0] # stationary
xiIndices = [0] # stationary
# %% We need to get the time stamps (in years here).
timeStamps = data[:, 0]
# %%
# We can now estimate the list of coefficients :math:`\vect{\beta} = (\beta_1, \beta_2, \beta_3, \beta_4)`
# using the log-likelihood of the data.
#
# We test the 3 normalizing methods and both initial points in order to evaluate their impact on the results.
# We can see that:
#
# - both normalization methods lead to the same result for :math:`\beta_1`, :math:`\beta_3` and :math:`\beta_4`
# (note that :math:`\beta_2` depends on the normalization function),
# - both initial points lead to the same result when the data have been normalized,
# - it is very important to normalize all the data: if not, the result strongly depends on the initial point
# and it differs from the result obtained with normalized data. The results are not optimal in that case
# since the associated log-likelihood are much smaller than those obtained with normalized data.
#
print("Linear mu(t) model:")
for normMeth in ["MinMax", "CenterReduce", "None"]:
for initPoint in ["Gumbel", "Static"]:
print(f"normMeth = {normMeth}, initPoint = {initPoint}")
# The ot.Function() is the identity function.
result = factory.buildTimeVarying(
sample,
timeStamps,
basis,
muIndices,
sigmaIndices,
xiIndices,
ot.Function(),
ot.Function(),
ot.Function(),
initPoint,
normMeth,
)
beta = result.getOptimalParameter()
print(f"beta = {beta}")
print(f"Max log-likelihood = {result.getLogLikelihood()}")
# %%
# According to the previous results, we choose the *MinMax* normalization method and the *Gumbel* initial point.
# This initial point is cheaper than the *Static* one as it requires no optimization computation.
result_NonStatLL = factory.buildTimeVarying(
sample,
timeStamps,
basis,
muIndices,
sigmaIndices,
xiIndices,
ot.Function(),
ot.Function(),
ot.Function(),
"Gumbel",
"MinMax",
)
beta = result_NonStatLL.getOptimalParameter()
print(f"beta = {beta}")
print(f"mu(t) = {beta[0]:.4f} + {beta[1]:.4f} * tau(t)")
print(f"sigma = {beta[2]:.4f}")
print(f"xi = {beta[3]:.4f}")
# %%
# You can get the expression of the normalizing function :math:`t \mapsto \tau(t)`:
normFunc = result_NonStatLL.getNormalizationFunction()
print("Function tau(t): ", normFunc)
print("c = ", normFunc.getEvaluation().getImplementation().getCenter()[0])
print("1/d = ", normFunc.getEvaluation().getImplementation().getLinear()[0, 0])
# %%
# You can get the function :math:`t \mapsto \vect{\theta}(t)` where :math:`\vect{\theta}(t) = (\mu(t), \sigma(t), \xi(t))`.
functionTheta = result_NonStatLL.getParameterFunction()
# %%
# We get the asymptotic distribution of :math:`\vect{\beta}` to compute some confidence intervals of
# the estimates, for example of order :math:`p = 0.95`.
dist_beta = result_NonStatLL.getParameterDistribution()
confidence_level = 0.95
for i in range(beta.getSize()):
lower_bound = dist_beta.getMarginal(i).computeQuantile((1 - confidence_level) / 2)[
0
]
upper_bound = dist_beta.getMarginal(i).computeQuantile((1 + confidence_level) / 2)[
0
]
print(
"Conf interval for beta_"
+ str(i + 1)
+ " = ["
+ str(lower_bound)
+ "; "
+ str(upper_bound)
+ "]"
)
# %%
# In order to compare different modelings, we get the optimal log-likelihood of the data for both stationary
# and non stationary models. The difference is significant enough to be in favor of the non stationary model.
print("Max log-likelihood: ")
print("Stationary model = ", result_LL.getLogLikelihood())
print("Non stationary linear mu(t) model = ", result_NonStatLL.getLogLikelihood())
# %%
# In order to draw some diagnostic plots similar to those drawn in the stationary case, we refer to the
# following result: if :math:`Z_t` is a non stationary GEV model parametrized by :math:`(\mu(t), \sigma(t), \xi(t))`,
# then the standardized variables :math:`\hat{Z}_t` defined by:
#
# .. math::
#
# \hat{Z}_t = \dfrac{1}{\xi(t)} \log \left[1+ \xi(t)\left( \dfrac{Z_t-\mu(t)}{\sigma(t)} \right)\right]
#
# have the standard Gumbel distribution which is the GEV model with :math:`(\mu, \sigma, \xi) = (0, 1, 0)`.
#
# As a result, we can validate the inference result thanks the 4 usual diagnostic plots:
#
# - the probability-probability pot,
# - the quantile-quantile pot,
# - the return level plot,
# - the data histogram and the density of the fitted model.
#
# using the transformed data compared to the Gumbel model. We can see that the adequation is better
# than with the stationary model.
graph = result_NonStatLL.drawDiagnosticPlot()
view = otv.View(graph)
# %%
# We can draw the mean function :math:`t \mapsto \Expect{\mbox{GEV}(t)}`. Be careful, it is not the function
# :math:`t \mapsto \mu(t)`. As a matter of fact, the mean is defined for :math:`\xi <1` only and in that case,
# for :math:`\xi \neq 0`, we have:
#
# .. math::
# \Expect{\mbox{GEV}(t)} = \mu(t) + \dfrac{\sigma(t)}{\xi(t)} (\Gamma(1-\xi(t))-1)
#
# and for :math:`\xi = 0`, we have:
#
# .. math::
# \Expect{\mbox{GEV}(t)} = \mu(t) + \sigma(t)\gamma
#
# where :math:`\gamma` is the Euler constant.
#
# We can also draw the function :math:`t \mapsto q_p(t)` where :math:`q_p(t)` is the quantile of
# order :math:`p` of the GEV distribution at time :math:`t`.
# Here, :math:`\mu(t)` is a linear function and the other parameters are constant, so the mean and the quantile
# functions are also linear functions.
graph = ot.Graph(
r"Annual maximum sea-levels at Fremantle - Linear $\mu(t)$",
"year",
"level (m)",
True,
"",
)
graph.setIntegerXTick(True)
# data
cloud = ot.Cloud(data[:, :2])
cloud.setColor("red")
graph.add(cloud)
# mean function
meandata = [
result_NonStatLL.getDistribution(t).getMean()[0] for t in data[:, 0].asPoint()
]
curve_meanPoints = ot.Curve(data[:, 0].asPoint(), meandata)
graph.add(curve_meanPoints)
# quantile function
graphQuantile = result_NonStatLL.drawQuantileFunction(0.95)
drawQuant = graphQuantile.getDrawable(0)
drawQuant = graphQuantile.getDrawable(0)
drawQuant.setLineStyle("dashed")
graph.add(drawQuant)
graph.setLegends(["data", "mean function", "quantile 0.95 function"])
graph.setLegendPosition("lower right")
view = otv.View(graph)
# %%
# At last, we can test the validity of the stationary model :math:`\mathcal{M}_0`
# relative to the model with time varying parameters :math:`\mathcal{M}_1`. The
# model :math:`\mathcal{M}_0` is parametrized by :math:`(\beta_1, \beta_3, \beta_4)` and the model
# :math:`\mathcal{M}_1` is parametrized by :math:`(\beta_1, \beta_2, \beta_3, \beta_4)`: so we have
# :math:`\mathcal{M}_0 \subset \mathcal{M}_1`.
#
# We use the Likelihood Ratio test. The null hypothesis is the stationary model :math:`\mathcal{M}_0`.
# The Type I error :math:`\alpha` is taken equal to 0.05.
#
# This test confirms that the dependence through time is not negligible: it means that the linear :math:`\mu(t)`
# component explains a large variation in the data.
llh_LL = result_LL.getLogLikelihood()
llh_NonStatLL = result_NonStatLL.getLogLikelihood()
modelM0_Nb_param = 3
modelM1_Nb_param = 4
resultLikRatioTest = ot.HypothesisTest.LikelihoodRatioTest(
modelM0_Nb_param, llh_LL, modelM1_Nb_param, llh_NonStatLL, 0.05
)
accepted = resultLikRatioTest.getBinaryQualityMeasure()
print(
f"Hypothesis H0 (stationary model) vs H1 (linear mu(t) model): accepted ? = {accepted}"
)
# %%
# We detail the statistics of the Likelihood Ratio test: the deviance statistics :math:`\mathcal{D}_p` follows
# a :math:`\chi^2_1` distribution.
# The model :math:`\mathcal{M}_0` is rejected if the deviance statistics estimated on the data is greater than
# the threshold :math:`c_{\alpha}` or if the p-value is less than the Type I error :math:`\alpha = 0.05`.
print(f"Dp={resultLikRatioTest.getStatistic():.2f}")
print(f"alpha={resultLikRatioTest.getThreshold():.2f}")
print(f"p-value={resultLikRatioTest.getPValue():.2f}")
# %%
# We can perform the same study with a quadratic model for :math:`\mu(t)` or a linear model for
# :math:`\mu(t)` and :math:`\sigma(t)`:
#
# .. math::
# :nowrap:
#
# \begin{align*}
# \mu(t) & = \beta_1 + \beta_2 \tau(t) + \beta_3\tau(t)^2 \\
# \sigma(t) & = \beta_4 \\
# \xi(t) & = \beta_5
# \end{align*}
#
# or
#
# .. math::
# :nowrap:
#
# \begin{align*}
# \mu(t) & = \beta_1 + \beta_2 \tau(t) \\
# \sigma(t) & = \beta_3 + \beta_4\tau(t)\\
# \xi(t) & = \beta_5
# \end{align*}
#
# For each model, we give the log-likelihood values and we test the validity of each model with respect
# to the non stationary model where :math:`\mu(t)` is linear.
# We notice that there is no evidence to adopt a quadratic model for :math:`\mu(t)` nor a linear model
# for :math:`\mu(t)` and :math:`\sigma(t)`: the optimal log-likelihood for each model is very near the likelihood
# we obtained with a linear model for :math:`\mu(t)` only. It means that these both models do not bring significant
# improvements with respect to model tested before.
basis = ot.Basis(
[constant, ot.SymbolicFunction(["t"], ["t"]), ot.SymbolicFunction(["t"], ["t^2"])]
)
result_NonStatLL_2 = factory.buildTimeVarying(
sample,
timeStamps,
basis,
[0, 1, 2],
[0],
[0],
ot.Function(),
ot.Function(),
ot.Function(),
"Gumbel",
"MinMax",
)
result_NonStatLL_3 = factory.buildTimeVarying(
sample,
timeStamps,
basis,
[0, 1],
[0, 1],
[0],
ot.Function(),
ot.Function(),
ot.Function(),
"Gumbel",
"MinMax",
)
print("Max log-likelihood = ")
print("Non stationary quadratic mu(t) model = ", result_NonStatLL_2.getLogLikelihood())
print(
"Non stationary linear mu(t) and sigma(t) model = ",
result_NonStatLL_3.getLogLikelihood(),
)
llh_LL = result_LL.getLogLikelihood()
llh_NonStatLL_2 = result_NonStatLL_2.getLogLikelihood()
llh_NonStatLL_3 = result_NonStatLL_3.getLogLikelihood()
resultLikRatioTest_2 = ot.HypothesisTest.LikelihoodRatioTest(
4, llh_NonStatLL, 5, llh_NonStatLL_2, 0.05
)
resultLikRatioTest_3 = ot.HypothesisTest.LikelihoodRatioTest(
4, llh_NonStatLL, 5, llh_NonStatLL_3, 0.05
)
accepted_2 = resultLikRatioTest_2.getBinaryQualityMeasure()
accepted_3 = resultLikRatioTest_3.getBinaryQualityMeasure()
print(
f"Hypothesis H0 (linear mu(t) model) vs H1 (quadratic mu(t) model): accepted ? = {accepted_2}"
)
print(
f"Hypothesis H0 (linear mu(t) model) vs H1 (linear mu(t) and sigma(t) model): accepted ? = {accepted_3}"
)
# %%
# **Non stationary GEV modeling with the covariates Time and SOI**
#
# Extreme sea-levels can be unusually extreme during periods when the El Nino effect is
# active.
# Hence, we study a modeling that takes into account the dependence between the extreme
# sea-levels
# at Fremantle and the annual mean value of the Southern Oscillation Index (SOI)
# besides the temporal dependence.
# The following figure shows that the annual maximum sea-levels are generally greater
# when the value of SOI is high. It might be due to the time trend in the data for the
# sea-levels
# and the SOI (each one increases with time). But it can also be possible that the
# SOI explains
# some of the variation in annual maximum sea-levels after allowance for the time variation
# in the process.
graph = ot.Graph("SOI at Fremantle", "SOI", "level (m)", True, "")
cloud = ot.Cloud(data.getMarginal([2, 1]))
cloud.setColor("red")
graph.add(cloud)
view = otv.View(graph)
# %%
# To consider this possibility, we study the model:
#
# .. math::
# :nowrap:
#
# \begin{align*}
# \mu(t) & = \beta_1 t + \beta_2 \mbox{SOI} + \beta_3 \\
# \sigma(t) & = \beta_4 \\
# \xi(t) & = \beta_5
# \end{align*}
#
# We consider two covariates: the time and the SOI. We build the sample of the values of both
# covariates: :math:`(t_i, \mbox{SOI}_i)_{1 \leq i \leq n}` where :math:`\mbox{SOI}_i =
# SOI(t_i)`.
# The constant covariate is
# automatically added by the library if not specified in order to allow
# some of the GEV parameters to remain constant (ie independent of both covariates
# :math:`(t, \mbox{SOI})`):
# this is the case for the :math:`\sigma` and :math:`\xi` parameters.
# This last constant covariate is associated to the
# third component of the covariates sample which now gathers the values
# :math:`(t_i, \mbox{SOI}_i, 1)` for :math:`1 \leq i \leq n`.
dataCovariates = data.getMarginal([0, 2])
print(dataCovariates[0:10])
result_Cov = factory.buildCovariates(sample, dataCovariates, [0, 1])
# %%
# We check here that a third component has effectively been added to the covariates
# sample: see the added third column which is constant equal to 1.
print(result_Cov.getCovariates()[0:10])
# %%
# We get the optimal parameter :math:`\vect{\beta}`.
beta = result_Cov.getOptimalParameter()
print("beta = ", beta)
# %%
# We get here the function :math:`(\vect{\beta}, t, \mbox{SOI}) \mapsto \vect{\theta}
# (\vect{\beta}, t, \mbox{SOI})` where :math:`\vect{\theta} = (\mu, \sigma, \xi)`. We see that
# :math:`\mu` depends on the three
# covariates :math:`(t, \mbox{SOI}, 1)` and that :math:`\sigma` and :math:`\xi` depends
# only on the third one
# which is the constant one.
print(result_Cov.getParameterFunction())
print(f"beta = {beta}")
print(f"mu(t) = {beta[0]:.4f} *t + {beta[1]:.4f} * SOI(t) + {beta[2]:.4f}")
print(f"sigma = {beta[3]:.4f}")
print(f"xi = {beta[4]:.4f}")
# %%
# We check here the normalizing function that has been used, which comes from
# the default method (the *MinMax* one).
print(result_Cov.getNormalizationFunction())
# %%
# We test this new model where :math:`\mu(t,SOI)` is modeled as a linear combination
# of the three covariates :math:`(t, \mbox{SOI}, 1)` against the model
# with the linear-trend only :math:`\mu(t)`. The maximized log-likelihood of this
# new model is 53.9, compared to 49.9 for the first model. Hence, the
# deviance statistics is equal to :math:`D = 8.0`, which is large when judged relative to
# a :math:`\chi_1^2` distribution.
# It provides evidence that the effect of SOI is influential on annual maximum
# sea-levels at Fremantle, even after the allowance for time-variation.
llh_cov = result_Cov.getLogLikelihood()
print("Max log-likelihood: ", llh_cov)
resultLikRatioTest_SOI = ot.HypothesisTest.LikelihoodRatioTest(
4, llh_NonStatLL, 5, llh_cov, 0.05
)
print(f"Dp={resultLikRatioTest_SOI.getStatistic():.2f}")
accepted = resultLikRatioTest_SOI.getBinaryQualityMeasure()
print(
f"Hypothesis H0 (linear-trend mu(t) model) vs H1 (linear-trend and SOI mu(t,SOI) model): accepted ? = {accepted}"
)
# %%
# We plot here the graphs :math:`t \mapsto \mu(t, \mbox{SOI}_0)` where
# :math:`\mbox{SOI}_0` is a given value (the mean value of the sample if not specified),
# and :math:`\mbox{SOI} \mapsto \mu(t_0, \mbox{SOI})` where :math:`t_0` is a given time.
# Care: there are three covariates :math:`(t, SOI, 1)` for the reasons mentioned previously.
# Then the reference point must be of dimension 3.
#
# As the relation is linear (the link function is the Identity function), we get some straight
# lines.
# The third graph is the dependence on the third covariate which is constant.
refSOI = dataCovariates.computeMean()[1]
refTime = 1940
refPoint = [refTime, refSOI, 1]
gridMu = result_Cov.drawParameterFunction1D(0, refPoint)
view = otv.View(gridMu)
# %%
# To adapt the labels and get rid of the last graph:
graphCol = gridMu.getGraphCollection()
graphMu1 = graphCol[0]
graphMu1.setTitle(r"$t \mapsto \mu(t, SOI_0)$, $SOI_0$ = {0:.2f}".format(refSOI))
graphMu1.setXTitle("t")
graphMu2 = graphCol[1]
graphMu2.setTitle(r"$SOI \mapsto \mu(t_0, SOI)$, $t_0 = $" + str(refTime))
graphMu2.setXTitle("SOI")
newGridLayout = ot.GridLayout(1, 2)
newGridLayout.setGraph(0, 0, graphMu1)
newGridLayout.setGraph(0, 1, graphMu2)
view = otv.View(newGridLayout)
# %%
# We plot here the graph :math:`(t, SOI) \mapsto \mu(t, SOI)`.
# As the third covariate is constant, the other graphs :math:`(t, 1)
# \mapsto \mu(t, \mbox{SOI}_0, 1)`
# and :math:`(1, SOI) \mapsto \mu(t_0, 1, SOI)` are not interesting
# as we have already obtained them with the previous method.
graphCol = result_Cov.drawParameterFunction2D(0, refPoint)
view = otv.View(graphCol)
# %%
# We plot here the graphs :math:`t \mapsto q_p(Z_{t, \mbox{SOI}_0})`
# and :math:`\mbox{SOI} \mapsto q_p(Z_{t_0, \mbox{SOI}})` where :math:`Z_{t, \mbox{SOI}_0}`
# is the process whose excesses of :math:`u` follow the estimated GPD,
# depending on the covariates :math:`(t, SOI)`. Then :math:`q_p`
# is the quantile of order :math:`p`.
# Because of the constant third covariate, the last graph is reduced to a point.
p = 0.95
gridQuantile = result_Cov.drawQuantileFunction1D(p, refPoint)
view = otv.View(gridQuantile)
# %%
# To adapt the labels and get rid of the last graph:
graphCol = gridQuantile.getGraphCollection()
graphQuant1 = graphCol[0]
graphQuant1.setTitle(r"$t \mapsto q_p(Z(t, SOI_0))$, $SOI_0$ = {0:.2f}".format(refSOI))
graphQuant1.setXTitle("t")
graphQuant1.setYTitle(r"$q_p$")
graphQuant2 = graphCol[1]
graphQuant2.setTitle(r"$SOI \mapsto q_p(Z(t_0, SOI))$, $t_0 = $" + str(refTime))
graphQuant2.setXTitle("SOI")
graphQuant2.setYTitle(r"$q_p$")
newGridLayout = ot.GridLayout(1, 2)
newGridLayout.setGraph(0, 0, graphQuant1)
newGridLayout.setGraph(0, 1, graphQuant2)
view = otv.View(newGridLayout)
# %%
otv.View.ShowAll()
|