preallocation?

i'm trying to solve for various parts of a compensated circuit, but some of my formulas are giving me this "preallocate" suggestion. i'm not sure how to do that, or if i need to. i looked it up on matlab help, but i'm unsure how to proceed. any suggestions? these are some of the variables that are giving the error message.

Prline (W)= (((abs(IlineRect))/(sqrt(2))^2)*Rline)
Prw (W)= (((abs(IlineRect))/(sqrt(2))^2)*Rw)
Prsns (W)= (((abs(IlineRect))/(sqrt(2))^2)*Rsns)
jQind (VAR)= (((abs(IlineRect))/(sqrt(2))^2)*jL)
Sload (VA)= (VldRect*(conj(IlineRect)))/2

Answer 1

[Walter Roberson]

Let numW be the maximum value that will be used for W, and numVA be the maximum value that will be used for VA, and numVAR be the maximum value that will be used for VAR. Then, before the loop that sets those variables,

Prline = zeros(1, numW);
Prw = zeros(1, numW);
Prsns = zeros(1, numW);
jQind = zeros(1, numVAR);
Sload = zeros(1, numVA);

By the way: if all of those variables are in the same loop and refer to the same IlineRect value, then calculate the common value only once:

   absIline2 = abs(IlineRect)^2 / 2;

Then

Prline(W) = absIline2 * Rline;
Prw(W) = absIline2 * Rw;

and so on.

Answer 2

[the cyclist]

I suggest you read this page from the documentation:

http://www.mathworks.com/help/techdoc/matlab_prog/f8-784135.html#f8-793781

Answer 3

[katerina jablonski]

yeah i saw that already. i need some more specific help.

Answer 4

[katerina jablonski]

okay i'll try that. thanks walter!!

[Walter Roberson]

See also my optimization suggestion that I edited into the above.