I = <\/span>...<\/span><\/span><\/div>
:<\/span><\/span><\/div><\/div>end<\/span><\/span><\/div><\/div>This had the advantage of not asking MATLAB to \"poof\" any variables into the workspace.  It helped also avoid situations where there was a possibility of a function and variable having the same name, thereby possibly not giving you the version of the name you expected.  The way you used <\/span>feval<\/span> at that time was generally via a character array identifying the function to be called. <\/span><\/div>I am only considering the use of <\/span>feval<\/span> in the context of characters or strings in MATLAB, and not for some of the more specialized versions such as working with GPUs.<\/span><\/div>You would call the integration function like this.<\/span><\/div>area = integ(<\/span>'myfun'<\/span>, 0, pi);<\/span><\/span><\/div><\/div>Today, with function handles, we can bypass using <\/span>feval<\/span> and use the function handle directly.<\/span><\/div>function <\/span>I=integ(fcn,fmin,fmax,tol)<\/span><\/span><\/div>if <\/span>~isa(fcn, <\/span>'function_handle'<\/span>)  <\/span><\/span><\/div>% might still be nice to allow chars for backward compatiblity- but not be permissive about allowing new \"strings\".<\/span><\/span><\/div>% if ~isa(fcn, 'function_handle') || ~ischar(fcn)<\/span><\/span><\/div>   error(<\/span>...<\/span>)<\/span><\/span><\/div>end<\/span><\/span><\/div>% figure out some initial points to evaluate<\/span><\/span><\/div>pts = linspace(fmin, fmax, 20);<\/span><\/span><\/div>fv = fcn(pts);<\/span><\/span><\/div>I = <\/span>...<\/span><\/span><\/div>:<\/span><\/span><\/div><\/div>end<\/span><\/span><\/div><\/div>Call it like this.<\/span><\/div>area = integ(@myfun, 0, pi);<\/span><\/span><\/div><\/div>This is useful for at least a couple of reasons: <\/span><\/div>It is generally faster, if only by a bit, because there is one less indirection of function calls.<\/span><\/li>
It evaluates the function for the handle you supply - and can't get confused about other possible name conflicts as a result.  Inside the integrator, we have complete control about the name of the function (called <\/span>fcn<\/span> in the code) and since it's a function handle, it can't conflict with anything else we may have around in the function or environment.<\/span><\/li><\/ul>Thoughts<\/span><\/h2>I know we use <\/span>feval<\/span> for some cases of working with GPUs, but I can't think of any typical MATLAB case where I still need to use <\/span>feval<\/span> instead of directly applying the function.  Do you still use <\/span>feval<\/span>, perhaps where it's no longer needed?  Let us know <\/span>here<\/span><\/a>.<\/span><\/div><\/img><\/div><\/span><\/div>Copyright 2022 The MathWorks, Inc.<\/span><\/div>\r\n