# How can i create a multivariable function from matrix data?

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Natanael Acencio Rijo il 4 Dic 2013
Commentato: sixwwwwww il 4 Dic 2013
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?
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Natanael Acencio Rijo il 4 Dic 2013
Modificato: Natanael Acencio Rijo il 4 Dic 2013
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.

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### Risposta accettata

sixwwwwww il 4 Dic 2013
Modificato: sixwwwwww il 4 Dic 2013
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)
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Natanael Acencio Rijo il 4 Dic 2013
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 il 4 Dic 2013
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()

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### Più risposte (1)

Andrei Bobrov il 4 Dic 2013
Totalcost= A(:)'*p(:);
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