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https://issues.apache.org/jira/browse/MATH-1657?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17707638#comment-17707638
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Gilles Sadowski commented on MATH-1657:
---------------------------------------
{quote}
{code:java}
double[] gradient = gradientOperator.operate(getObjectiveFunction())
{code}
{quote}
A {{getObjectiveFunction()}} method would indeed allow circumventing the
counting (thus breaking the promise of that part of the API).
Isn't the [current
API|https://commons.apache.org/proper/commons-math/javadocs/api-4.0-beta1/org/apache/commons/math4/legacy/optim/nonlinear/scalar/ObjectiveFunctionGradient.html]
covering that case (see e.g.
[NonLinearConjugateGradientOptimizer|https://commons.apache.org/proper/commons-math/javadocs/api-4.0-beta1/org/apache/commons/math4/legacy/optim/nonlinear/scalar/gradient/NonLinearConjugateGradientOptimizer.html#parseOptimizationData(org.apache.commons.math4.legacy.optim.OptimizationData...)])?
> Enhance management the objective function of optimizer
> ------------------------------------------------------
>
> Key: MATH-1657
> URL: https://issues.apache.org/jira/browse/MATH-1657
> Project: Commons Math
> Issue Type: Improvement
> Components: legacy
> Affects Versions: 4.0-beta1
> Reporter: François Laferrière
> Priority: Minor
>
> In MultivariateOptimizer class, objective function is not accessible once
> set: only computeObjectiveValue(double[] params) allows to access the value.
> This is probably to ensure that the evaluation counter is always properly
> incremented.
> But it is not very convenient for my purpose where I need to apply operators
> to the function. For instance
> {code:java}
> double[] gradient = gradientOperator.operate(getObjectiveFunction())
> {code}
> I suggest to wrap the function into an anonymous MultivariateFunction at
> setting time:
> {code:java}
> protected void setObjectiveFunction(MultivariateFunction func) {
> function = new MultivariateFunction() {
> @Override
> public double value(double[] point) throws
> IllegalArgumentException {
> incrementEvaluationCount();
> return func.value(point);
> }
> };
> }
> {code}
> So that we can still have at least a protected accessor
> {code:java}
> protected MultivariateFunction getObjectiveFunction() {
> return function;
> }
> {code}
> This is only an extension that has no impact on current API.
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