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########################################################################
##
## Copyright (C) 2006-2024 The Octave Project Developers
##
## See the file COPYRIGHT.md in the top-level directory of this
## distribution or <https://octave.org/copyright/>.
##
## This file is part of Octave.
##
## Octave is free software: you can redistribute it and/or modify it
## under the terms of the GNU General Public License as published by
## the Free Software Foundation, either version 3 of the License, or
## (at your option) any later version.
##
## Octave is distributed in the hope that it will be useful, but
## WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
## GNU General Public License for more details.
##
## You should have received a copy of the GNU General Public License
## along with Octave; see the file COPYING. If not, see
## <https://www.gnu.org/licenses/>.
##
########################################################################
## -*- texinfo -*-
## @deftypefn {} {@var{retval} =} ode_event_handler (@var{@@evt_fcn}, @var{t}, @var{y}, @var{k_vals}, @var{ord}, @var{flag})
##
## Return the solution of the event function (@var{@@evt_fcn}) which is
## specified in the form of a function handle.
##
## The second input argument @var{t} is a scalar double and specifies the time
## of the event evaluation.
##
## The third input argument @var{y} is a scalar or a column vector of type
## double which specifies the solution(s) at time @var{t}.
##
## The fourth input argument @var{k_vals} is a vector or matrix with the
## k values obtained from the most recent integration step.
##
## The fifth input argument @var{ord} the order of the integration technique.
##
## The sixth input argument @var{flag} is of type string. Valid values are:
##
## @table @option
## @item @qcode{"init"}
## Initialize internal persistent variables of the function
## @code{ode_event_handler} and return an empty cell array of size 4.
##
## @item @qcode{""}
## (default) Evaluate the event function and return the solution @var{retval}
## as a cell array of size 4. Inputs @var{ord} and @var{@@evt_fcn} are ignored,
## since they are set in the @qcode{"init"} step.
##
## @item @qcode{"done"}
## Clean up internal variables of the function @code{ode_event_handler} and
## return an empty cell array of size 4. All other inputs are ignored with
## this flag.
## @end table
##
## This function is an ODE internal helper function and it should never be
## necessary to call it directly.
## @end deftypefn
function retval = ode_event_handler (evt_fcn, t, y, k_vals, ord, flag = "")
## No error handling has been implemented in this function to achieve
## the highest performance possible.
## retval{1} is true (to terminate) or false (to continue)
## retval{2} is the index information for which an event occurred
## retval{3} is the time information column vector
## retval{4} is the line by line result information matrix
## These persistent variables store the results and time value from the
## processing in the previous time stamp.
## evtold the results from the event function
## told the time stamp
## yold the ODE result
## retcell the return values cell array
## evtcnt the counter for how often this function has been called
persistent evtold told yold retcell order evtfcn;
persistent evtcnt = 1; # Don't remove. Required for Octave parser.
persistent firstrun = true;
if (isempty (flag))
## Process the event, i.e.,
## find the zero crossings for either a rising or falling edge
[evt, term, dir] = evtfcn (t, y);
## We require that all return values be row vectors
evt = evt(:).'; term = term(:).'; dir = dir(:).';
## Check if one or more signs of the event has changed
signum = (sign (evtold) != sign (evt));
if (any (signum)) # One or more values have changed
## Find events where either rising and falling edges are counted (dir==0)
## or where the specified edge type matches the event edge type.
idx = signum & (dir == 0 | dir == sign (evt));
idx = find (idx); # convert logical to numeric index or []
## Create new output values if a valid index has been found
if (! isempty (idx))
## Change the persistent result cell array
if (firstrun)
## Matlab compatibility requires ignoring condition on first run.
retcell{1} = false;
else
retcell{1} = any (term(idx)); # Stop integration or not
endif
evtcntnew = 1;
## Add all events this step to the output.
for idx2 = idx # Loop through all values of idx
## Calculate the time stamp when the event function returned 0 and
## calculate new values for the integration results. We do both by
## root solving, calling the Event function with y values from
## the RK interpolation polynomial. Set tolerance to zero (actually
## uses machine tolerance based criterion in this case) since we
## don't have a way for the user to specify an acceptable tolerance.
## For simple Event functions, this means we're basically root
## finding on a small interval for a polynomial, so we expect
## pretty quick convergence.
tvals = [told t];
yvals = [yold y];
tnew = fzero(@(t2) evtfcn_val (evtfcn, t2, ...
runge_kutta_interpolate (order, tvals, yvals, ...
t2, k_vals), idx2), tvals, optimset ("TolX", 0));
ynew = runge_kutta_interpolate (order, tvals, yvals, tnew, k_vals);
tnews(evtcntnew, 1) = tnew;
ynews(evtcntnew, :) = ynew;
terms(evtcntnew, 1) = term(idx2);
evtcntnew += 1;
endfor
## Sort by time of event
if (length (idx) > 1)
[tnews, idx_sort] = sort (tnews, "ascend");
idxs = idx(idx_sort);
ynews = ynews(idx_sort,:);
terms = terms(idx_sort);
else
idxs = idx;
endif
## Check for terminal events and remove any events after terminal.
## Any events at same time as first terminal event will be retained.
idx3 = find (terms, 1); # Find first terminal event by time
if (! isempty (idx3))
t_cutoff = tnews(idx3);
## Last index to return
evtcntnew = find (tnews == t_cutoff, 1, "last");
else
evtcntnew = length (terms); # Return all indices if no terminal
endif
idxs = idxs(1:evtcntnew);
tnews = tnews(1:evtcntnew);
## Populate return values with sorted, clipped values
evtcntrange = evtcnt - 1 + (1:evtcntnew);
evtcnt += evtcntnew;
retcell{2}(evtcntrange, 1) = idxs(:);
retcell{3}(evtcntrange, 1) = tnews(:);
retcell{4}(evtcntrange, :) = ynews(1:evtcntnew,:);
endif
endif
firstrun = false;
evtold = evt; told = t; yold = y;
retval = retcell;
elseif (strcmp (flag, "init"))
## Call the event function if an event function has been defined to
## initialize the internal variables of the event function and to get
## a value for evtold.
firstrun = true;
order = ord;
evtfcn = evt_fcn;
[evtold, ~, ~] = evtfcn (t, y);
## We require that all return values be row vectors
evtold = evtold(:).'; told = t; yold = y;
evtcnt = 1;
retval = retcell = cell (1,4);
elseif (strcmp (flag, "done"))
## Clear this event handling function
firstrun = true;
evtold = told = yold = evtcnt = order = evtfcn = [];
retval = retcell = cell (1,4);
endif
endfunction
function val = evtfcn_val (evtfcn, t, y, ind)
[evt, ~, ~] = evtfcn (t, y);
val = evt(ind);
endfunction
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