Create function output seperately

Hello!

I am curious if this is possible. Say I write a function

function F = func(x)
   F(1) = x(1)-cos(x(2));
   F(2) = x(2)-cos(x(1));
end

Now every time I call on this function it calculates the RHS of the equation and gives an output for F. Now if I had a ton of calculations before F that I don't want Matlab to constantly repeat, all I want is the last statement F.

An example would be

function F = func(x)
   % I send the x vector in order to get boundary conditions
   BC = Boundaries(x);
   % Now BC is a function with equations like BC(1) =  x(1)+x(2)... etc
   F(1) = BC(1);
   F(2) = BC(2);
end

I want to use the function F(1) = x(1)+x(2), and not have to constantly send x to BC to "create" those equations.

[Guillaume]

I'm afraid I don't really understand what you're asking. What does to "create" those equations actually mean?

You can pass a function to use to another function if that's what you're after (i.e. you could pass different BC functions to func).

[Kristoffer Lindvall]

Yes, the point is that every time I call on func(x) Matlab sends the x values to BC as well, and then to F. I would like to be able to create functions somewhere else once, and then set F equal to those functions, then have Matlab only evaluate F.

Imagine if the BC function takes a lot of CPU time to create the equations x(1)+x(2)... etc. I only want the result of BC. I don't want to go through the process of making BC. As far I have understood it, Matlab goes through BC every time I need to evaluate F. Even if I create BC somewhere else, it still goes through BC and all that that function has inside it to output a result.

I think the problem is that the function isn't creating equations, but more like a path that x values go through. This is really hard to explain I apologize.

[Dennis]

You can create BC once and then pass it to func:

BC=Boundaries(2); %creating BC once
F=func(1:3,BC);

function BC=Boundaries(x)
BC=1:3+x; %some heavy calculations
end

function F=func(x,BC) %passing BC aswell
F(1)=BC(1)+x(2);
end

[Stephen23]

Then why not just move Boundaries outside of func and calculate it only once?

[Guillaume]

Still not entirely clear on what is being asked, not helped by the imprecise terms used. You don't make functions. Functions don't create equations. You call a function with some inputs and it returns some outputs.

In addition to what has already been suggested, since R2017a, there is also the possibility of memoizing a function, a technique that caches the results of a function that is expensive to run so that it is only run if different inputs are provided. No idea, if that's what you're after.