For loop - what about my min and max values?

Tom (view profile)

on 11 Dec 2011
Accepted Answer by bym

bym (view profile)

For loop - what about my min and max values? I'm using a for loop and although my plot is right, I'm only seeing my maximum x-axis value in the Workspace Max column. Is there a way to have the Min and Max columns actually correct?
Many thanks
iter=1;
for f=50:1000
rho_a=1.2041;
sigma=11000;
phi=0.99;
alpha=1;
c=343.26;
i=sqrt(-1);
L=0.1;
a=0.03;
k_a=(2*pi*f)/c;
k_2=((2*pi*f)/c)*sqrt(alpha-((i*sigma*phi)/(2*pi*f*rho_a)));
z_c_2=((rho_a*c)/phi)*sqrt(alpha-((i*sigma*phi)/(2*pi*f*rho_a)));
z_1=(z_c_2*cot(k_2*L)*(cos(k_a*a)+(i/(rho_a*c))*sin(k_a*a)))/(i*cos(k_a*a)-(1/(rho_a*c))*sin(k_a*a));
R=((z_1/(rho_a*c))-1)/(1+(z_1/(rho_a*c)));
Rrec(iter)=R;
AbsCoef=1-(real(R))^2;
AbsCoefrec(iter)=AbsCoef;
z_1rec(iter)=z_1;
iter=iter+1;
end
plot(50:1000,AbsCoefrec)

Jan

Jan (view profile)

on 11 Dec 2011
What is "the maximum x-axis value" and what is the "Workspace Max column"? And how is the correctness of the "Min and Max columns" defined? What the is the relation between the question and the code?
To improve the code (dramatically!) look in this forum for the term "pre-allocation".
David Young

David Young (view profile)

on 11 Dec 2011
i is already defined in Matlab - as long as you haven't redefined it earlier in the program you don't need to do i = sqrt(-1)

bym (view profile)

on 11 Dec 2011

Your x axis is the loop variable f, which can only take on one value at a time, thus the min and max are the same. To do what you want, you would have to modify your code something like this
freq = 50:1000;
AbsCoefrec = zeros(size(freq)); % preallocate!
for f = freq
% ---insert code here---
end
plot(freq,AbsCoefrec)

Tom

Tom (view profile)

on 11 Dec 2011
right okay. is req the same as rec?
many thanks for that