- Aide de Scilab
- Optimisation et Simulation
- Optimization base
- optimbase_cget
- optimbase_checkbounds
- optimbase_checkcostfun
- optimbase_checkx0
- optimbase_configure
- optimbase_destroy
- optimbase_function
- optimbase_get
- optimbase_hasbounds
- optimbase_hasconstraints
- optimbase_hasnlcons
- optimbase_histget
- optimbase_histset
- optimbase_incriter
- optimbase_isfeasible
- optimbase_isinbounds
- optimbase_isinnonlincons
- optimbase_log
- optimbase_new
- optimbase_outputcmd
- optimbase_outstruct
- overview
- optimbase_proj2bnds
- optimbase_set
- optimbase_stoplog
- optimbase_terminate
Please note that the recommended version of Scilab is 2024.1.0. This page might be outdated.
See the recommended documentation of this function
optimbase_terminate
Checks if the algorithm is terminated.
Calling Sequence
[opt, terminate, status] = optimbase_terminate(opt, previousfopt, currentfopt, previousxopt, currentxopt)
Argument
- opt
The object of TOPTIM type (tlist).
- previousfopt
A vector of doubles, the previous value of the cost function.
- currentfopt
A vector of doubles, the current value of the cost function.
- previousxopt
A vector of doubles, the previous x optimum.
- currentxopt
A vector of doubles, the current x optimum.
- terminate
A boolean.
terminate = %t if the algorithm must terminate.
terminate = %f if the algorithme must continue.
- status
A string.
If
terminate
= %t, the detailed status of the termination corresponds to :- "maxiter"
- The maximum number of iterations, provided by the
-maxiter
option, is reached. - "maxfuneval"
- The maximum number of function evaluations, provided by the
-maxfunevals
option, is reached. - "tolf"
- The tolerance on the function value is reached. This status is associated
with the
-tolfunmethod
,-tolfunabsolute
and-tolfunrelative
options. - "tolx"
- The tolerance on x is reached. This status is associated with the
-tolxmethod
,-tolxabsolute
and-tolxrelative
options.
Description
The optimbase_terminate
function returns a boolean:
%t if the algorithm is terminated,
%f if the algorithm must continue.
If the -verbosetermination
option is enabled, messages are printed
detailing the termination intermediate steps.
The optimbase_terminate
function uses a set of rules to compute if
the termination occurs, which leads to an optimization status which is equal to one of
the following: "continue", "maxiter", "maxfunevals", "tolf", "tolx". The set of rules
is the following.
By default, the status is "continue", and the terminate flag is %f.
The number of iterations is examined and compared to the
-maxiter
option. If the following conditioniterations >= maxiter
is true, then the status is set to "maxiter" and terminate is set to %t.
The number of function evaluations and compared to the
-maxfunevals
option is examined. I the following conditionfunevals >= maxfunevals
is true, then the status is set to "maxfunevals" and terminate is set to %t.
The tolerance on function value is examined depending on the value of the
-tolfunmethod
option.- "disabled"
then the tolerance on f is just skipped.
"enabled"
if the following condition
is true, then the status is set to "tolf" and terminate is set to %t.
The relative termination criteria on the function value works well if the function value at optimum is near zero. In that case, the function value at initial guess
fx0
may be used as previousfopt.The absolute termination criteria on the function value works if the user has an accurate idea of the optimum function value.
The tolerance on
x
is examined depending on the value of the-tolxmethod
otpion.- %f
then the tolerance on x is just skipped.
%t
if the following condition
is true, then the status is set to "tolx" and terminate is set to %t.
The relative termination criteria on x works well if x at optimum is different form zero. In that case, the condition measures the distance between two iterates.
The absolute termination criteria on x works if the user has an accurate idea of the scale of the optimum x. If the optimum x is nea 0, the relative tolerance will not work and the absolute tolerance is more appropriate.
Example
In the following example, ones searches to solve f(x) = 0 thanks dichotomy method.
An optimization object is created and configured (number of variables, initial point,
maximum number of iterations, ...). The -verbose
option is enabled so that
messages are generated during the algorithm, are printed.
function [f, index]=fun(x, index) f = 2*x - 4; endfunction a = -5; b = 5; x0 = (a+b)/2; // Creation of the object opt = optimbase_new(); // Configures the object opt = optimbase_configure(opt,"-numberofvariables",2); opt = optimbase_configure(opt, "-x0", x0); opt = optimbase_configure(opt, "-tolxrelative", 10*%eps); opt = optimbase_configure(opt, "-maxiter", 30); opt = optimbase_configure(opt, "-function", fun); opt = optimbase_configure(opt,"-verbose",1); function x=Dicho(opt, a, b) xk = optimbase_cget(opt, "-x0"); [opt, fx0, index] = optimbase_function (opt , xk , 1); opt = optimbase_set ( opt , "-xopt" , xk ); opt = optimbase_set ( opt , "-fopt" , fx0 ); terminate = %f; while ~terminate [opt, f, index] = optimbase_function(opt, xk, 1); [opt, g, index] = optimbase_function(opt, a, 1); if g*f <= 0 then b = xk; else a = xk; end x = (a + b)/2; opt = optimbase_incriter(opt); [opt, terminate, status] = optimbase_terminate(opt, optimbase_get(opt, "-fopt"), f, xk, x); opt = optimbase_set ( opt , "-xopt" , x ); opt = optimbase_set ( opt , "-fopt" , f ); xk = x; end endfunction x = Dicho(opt,a,b)
See Also
- optimbase_function — Calls cost function.
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