How can i create a multivariable function from matrix data?

Hi i´m new to matlab. Im trying to create a program that reads data out of a matrix and assigns those values to variables. the issue is that this must be a function for which im going to evaluate its minima, so i cannot define p.

My problem is of this kind:

im going to evaluate the minimum value possible of p

A=[150;

   200;

   300;]

I want to generate this from the previous data:

f(1)=A(1,1)*p(1)

f(2)=A(2,1)*p(2)

f(3)=A(3,1)*p(3)

resulting at the end that

Totalcost= f(1)+f(2)+f(3); which will a multivariable function.

I tried to use a for loop in this case but it doesnt let me assign the values in the parenthesis to the p, to make it a different variable. it keeps telling me that i´m reffering to a value that has been cleared.

what i want to know is: which commands can i use to assign values to the p as a variable of a multivariable function?

[Natanael Acencio Rijo]

I finally got the result for the function to minimize, but it´s still in sym class, so it doesnt let me evaluate it for optimization. but it doesnt let me convert the variables p to double class, so that the optimization algorithm can input values in it.

Answer 1

[sixwwwwww]

if you have symbolic toolbox installed then you can do it as follows:

A = [150; 200; 300]; 
p = sym('p%d', [1 numel(A)]);
for i = 1:numel(A)
    f(i) = A(i) * p(i);
end
Totalcost = sum(f(:));
disp(Totalcost)

[Natanael Acencio Rijo]

I finally got the result for the function to minimize, but it´s still in sym class, so it doesnt let me evaluate it for optimization. but it doesnt let me convert the variables p to double class, so that the optimization algorithm can input values in it.

[sixwwwwww]

You can use

double(YourSymbolicValue)

and it will convert the symbolic value into double type value which you can use further in your code. See for more information:

http://www.mathworks.com/help/matlab/ref/double.html

[Natanael Acencio Rijo]

I tried that already it keeps telling me this:

The following error occurred converting from sym to double: Error using mupadmex Error in MuPAD command: DOUBLE cannot convert the input expression into a double array. If the input expression contains a symbolic variable, use the VPA function instead.

using VPA just deals with the coefficients. Hopefully I´ll get outta this. Thanks..

[sixwwwwww]

can you show me your code? to properly figure out

[Natanael Acencio Rijo]

function cost= cost(p) ;

clc

clear

costfunctionsetting;

sizel=size(CostFormulavariables);

alpha=CostFormulavariables(:,1);

beta=CostFormulavariables(:,2);

gamma=CostFormulavariables(:,3);

syms p(k)

for k = 1:sizel;

f(k)=(alpha(k,1)+(beta(k,1)*p(k))+(gamma(k,1)*p(k)^2));

end

cost=vpa(sum(f))

end

[Natanael Acencio Rijo]

ans =

5.3*p(1) + 5.5*p(2) + 5.8*p(3) + 0.004*p(1)^2 + 0.006*p(2)^2 + 0.009*p(3)^2 + 1100.0

this is my final result, what i want to do then is being able to find its minimum, but it is in sym class and the optimization toolbox doesnt accept the variables.

[sixwwwwww]

you need to subsitutute values for symbols p(1), p(2), ... then you can get numeric values in symbols which you can convert to double type using doouble()

Answer 2

[Andrei Bobrov]

Totalcost= A(:)'*p(:);