How to call fminsearch on my function

Hello everyone,

Currently working on a class project and could really use some help using fminsearch. I have modeled a refrigeration cycle in matlab. Now I need to optimize the code I have written to find minmum values as a part of a new assignment. The function I want to optimize is

function[W,X,LH2]=refrig(PR,PC)

however within this code there are multiple components that get called from other scripts. When I try to use

x0 = [100,0.4]

fminsearch('refrig',x0)

I get an output saying that I don't have enough input arguments because of the lack of input arguments for parts of the function which calls other scripts. However when I just run the code as

refrig(100,0.4)

it runs just fine with no errors. How can I call fminsearch for a function like this?

Answer 1

[John D'Errico]

Um, you misunderstand the problem. Your function has TWO arguments. PR and PC, both of which you want to be optimized. And while you think this is how fminsearch will work, you would be wrong.

fminsearch is passed a VECTOR of length 2 as the initial parameters. It will then pass in a VECTOR of length 2 to your funcrtion, NOT two distinct arguments. Your function needs to recognize that.

So you can either unpack that vector into PR and PC in your function, you can write a wrapper function around it. Something like this:

wrapper = @(PRPC) refrig(PRPC(1),PRPC(2));

Now you will use fminsearch on the function wrapper. It will then call refrig, splitting the parameters into TWO separate arguments.

Note that fminsearch will minimize the first output of refrig, thus W. It could care less about the other outputs.

[Francis Dunne]

Thank you! I see what you are saying about the vector of length 2. Sorry I'm new to matlab so I also have a question about the wrapper function. Do I make a new script wrapper.m and then call that in fminsearch in a seperate file?

[Walter Roberson]

You do not need to create wrapper.m . You can just use the assignment that John shows.

wrapper = @(PRPC) refrig(PRPC(1),PRPC(2));
fminsearch(wrapper,x0)

[Francis Dunne]

Ok. The last bit I don't understand is what do assign x0 as? Still just a vector of length two?

[Walter Roberson]

Yes, a vector of length 2.