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
|
/*
* Copyright (c) 1995 David I. Bell
* Permission is granted to use, distribute, or modify this source,
* provided that this copyright notice remains intact.
*
* Solve the equation f(x) = 0 to within the desired error value for x.
* The function 'f' must be defined outside of this routine, and the low
* and high values are guesses which must produce values with opposite signs.
*/
define solve(low, high, epsilon)
{
local flow, fhigh, fmid, mid, places;
if (isnull(epsilon))
epsilon = epsilon();
if (epsilon <= 0)
quit "Non-positive epsilon value";
places = highbit(1 + int(1/epsilon)) + 1;
flow = f(low);
if (abs(flow) < epsilon)
return low;
fhigh = f(high);
if (abs(flow) < epsilon)
return high;
if (sgn(flow) == sgn(fhigh))
quit "Non-opposite signs";
while (1) {
mid = bround(high - fhigh * (high - low) / (fhigh - flow), places);
if ((mid == low) || (mid == high))
places++;
fmid = f(mid);
if (abs(fmid) < epsilon)
return mid;
if (sgn(fmid) == sgn(flow)) {
low = mid;
flow = fmid;
} else {
high = mid;
fhigh = fmid;
}
}
}
if (config("lib_debug") >= 0) {
print "solve(low, high, epsilon) defined";
}
|
