Inconveniences working with matlabFunction

Hello,

I think that I am repeating the same sort of question I bothered you yesterday but I did not expect to run into peoblem again. Consider the following:

>> syms x y

>> g=[x*y y^2;x^3 1-x^2];

>> G=matlabFunction(g)

G =

function_handle with value:

@(x,y)reshape([x.*y,x.^3,y.^2,-x.^2+1.0],[2,2])

I am not happy with this. I would prefer the 'reshape' to be removed. Why? because this is never convenient in letting me to to do vector operations. For instance, if I use the command G([1 1],[1 1]) then matlab throws an erros message. How can I tell matlab PLEASE make the following matlab function for me:

G=(x,y)[x.*y,x.^3,y.^2,-x.^2+1.0];

In my codes G (different G, of course) is the Hessian matrix and I need to use it for my optimization problem in order to get faster and more accurate solutions.

Thanks for your kind help, in advance!

Babak

Answer 1

[Star Strider]

The reshape argument simply takes the vector of argumentsin the square brackets [] and creates a matrix from them, as required. One option is to use arrayfun. However, it wil then interpret its inputs as —

GL([x(1) x(2)],[y(1) y(2)])

So changing the arguments so you and the function agree on how they should be claculated will be necessary, regardless of the funciton version you end up using —

G = @(x,y)reshape([x.*y,x.^3,y.^2,-x.^2+1.0],[2,2]);        % 'matlabFunction' Result
GL = @(xv,yv) arrayfun(G, xv,yv, 'Unif',0);
V = GL([1 2],[3 4])

V = 1×2 cell array
    {2×2 double}    {2×2 double}

V{1}

ans = 2×2

3 9 1 0

V{2}

ans = 2×2

8 16 8 -3

G2 = @(x,y)[x.*y y.^2; x.^3 1-x.^2];                      % Your Original Function (Vectorised)
V = G2([1 2],[3 4])

V = 2×4

3 8 9 16 1 8 0 -3

G2L = @(xv,yv) arrayfun(G2, xv,yv, 'Unif',0);
V2 = G2L([1 2],[3 4])

V2 = 1×2 cell array
    {2×2 double}    {2×2 double}

V2{1}

ans = 2×2

3 9 1 0

V2{2}

ans = 2×2

8 16 8 -3

Both end up producing the same result.

.

[Torsten]

@Mohammad Shojaei Arani comment moved here:

Thanks Star!

This solves my problem.

[Star Strider]

@Mohammad Shojaei Arani — As always, my pleasure!

@Torsten — Thank you!

[Mohammad Shojaei Arani]

Hello,

Thanks Star for your kind response. But, I ran into a similar problem again (you correctly answered my previous question). Consider the following

>> syms x y p1 p2

h=[x*y+p1 y^2-1;x^3+p2^2 1-x^2+p1*p2];

H=matlabFunction(h)

H =

function_handle with value:

@(p1,p2,x,y)reshape([p1+x.*y,p2.^2+x.^3,y.^2-1.0,p1.*p2-x.^2+1.0],[2,2])

I am not happy with this. I would prefer the 'reshape' to be removed. Why? because this is never convenient in letting me to to do vector operations. For instance, if I use the command H(1,2,[3 4],[5 6]) then matlab throws an erros message. How can I tell matlab PLEASE make the following matlab function for me:

H=@(p1,p2,x,y)[x*y+p1 y^2-1;x^3+p2^2 1-x^2+p1*p2];

I know how to tackle this problem when all inputs p1,p2,x,y have the same size (I can fix it by the command HL = @(p1v,p2v,xv,yv) arrayfun(H, p1v,p2v,xv,yv, 'Unif',0);).

However, here p1 and p2 are scalar parameters while x and y are (row) vectors of the same size (like H(1,2,[3 4],[5 6]), as I mentioned above). The best way to tackle this problem for me is as follows:

I would prefer the output to be a 3D array where the first page is H(1,2,3,5) and the second page is H(1,2,4,6).

Thanks for your kind help, in advance!

Babak

[Star Strider]

This is an application of passing extra parameters. As such, it now needs a separate function call in order to work correctly.

Try this —

Hmtx = cat(3, Hfcn(1,2,3,5), Hfcn(1,2,4,6))

Hmtx = 
Hmtx(:,:,1) =

    16    24
    31    -6


Hmtx(:,:,2) =

    25    35
    68   -13

function M = Hfcn(p1,p2,v1,v2)
    H = @(p1,p2,x,y)reshape([p1+x.*y,p2.^2+x.^3,y.^2-1.0,p1.*p2-x.^2+1.0],[2,2]);
    C = arrayfun(@(xv,yv)H(p1,p2,xv,yv),v1,v2, 'Unif',0);
    M = cell2mat(C);
end

.

[Mohammad Shojaei Arani]

Thanks Star,

Thanks for your kind help!

Babak

[Star Strider]

As always, my pleasure!