"isfield" for hidden field in optimoptions

hi,

with Matlab 2019 it seems that:

options = optimoptions(@fsolve,'JacobPattern',speye(5))
isfield(options,'JacobPattern')

will return 0. But options.JacobPattern will return the speye(5).

I guess this is due to the hidden nature of JacobPattern. I want the code to check if the field is specified or not.

How do I do that?

Answer 1

[Walter Roberson]

optimoptions returns on object of class optim.options.Fsolve not a struct.

You need to use

isprop(options,'JacobPattern')

However, more likely is that you want

isprop(options,'JacobPattern') && ~strcmp(options.JacobPattern), 'sparse(ones(Jrows,Jcols))')

[Stephen23]

The design decision for "If S is not a structure array, then isfield returns 0" baffles me. It seems to generate plenty of confusion (such as this question) but has precious few use-cases. Why not simply throw an error?

[Walter Roberson]

I dunno. It is documented though

If S is not a structure array, then isfield returns 0.

I guess it makes it marginally easier to handle the situation where a function returns either a structure array or else []

[Stephen23]

Such situations are also easily handled by the user: isstruct(S) && isfield(S,..)

Answer 2

[Matt J]

One way:

options = optimoptions(@fsolve,'JacobPattern',speye(5));

isNonDefault = ~isequal(options.JacobPattern,  optimoptions(@fsolve).JacobPattern )

isNonDefault = logical
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