Might be growing inside the loop. Consider Prealocating for Speed - matlab

Question

clear all
k_1 = 37.6;
miu_1 = 41;
Den = 2.7;
N = 100;
n=1;
phi(1)=1;
for n=1:N
phi(n)= 0.3*(n/N);
K_s(n)= K_1*(1-(1+(3*k_1)/(4*miu_1))*phi(n));
miu_s(n)= miu_1*(1-(1+(3*k_1)/(4*miu_1))*phi(n));
den1(n)=Den*(1-phi(n));
vp(n)=sqrt((k_s(n)+(4/3)*miu_s(n))/den1(n));
end
figure(1);
plot(phi,miu_s);
figure(2);
plot (phi,vp)
i am new on matlab and do not know what is problem with my code when i run my program only a beep buzz and nothing happens. guide me

Answer 1

The reason your code doesn't work is case sensitivity. You are using k_1 and K_1, and k_s and K_s (unless that is intentional). When I change that, your code compiles ok.
clear all
k_1 = 37.6;
miu_1 = 41;
Den = 2.7;
N = 100;
n=1;
phi(1)=1;
for n=1:N
phi(n)= 0.3*(n/N);
k_s(n)= k_1*(1-(1+(3*k_1)/(4*miu_1))*phi(n));
miu_s(n)= miu_1*(1-(1+(3*k_1)/(4*miu_1))*phi(n));
den1(n)=Den*(1-phi(n));
vp(n)=sqrt((k_s(n)+(4/3)*miu_s(n))/den1(n));
end
figure(1);
plot(phi,miu_s);
figure(2);
plot (phi,vp)

Answer 2

when programming in MatLab, is usually a good practice to prealocate variables instead of declaring them in a loop. In this way, MatLab creates the object just once and changes each of it's values once in the loop. Otherwise you will be declaring a new variable and writing all its contents every loop iteration which is a costly process. Your Code might be working but be extreeeeemly slow, leading you to think nothing is happening. Try prealocating all the variables inside the loop with the zeros() function like this:
phi=zeros(N,1);
phi(1)=1;
K_s=zeros(N,1);
%... and so on for all your variables inside the loop
for n=1:N
phi(n)= 0.3*(n/N);
K_s(n)= k_1*(1-(1+(3*k_1)/(4*miu_1))*phi(n));
miu_s(n)= miu_1*(1-(1+(3*k_1)/(4*miu_1))*phi(n));
den1(n)=Den*(1-phi(n));
vp(n)=sqrt((k_s(n)+(4/3)*miu_s(n))/den1(n));
end
Hope that helps

Answer 3

You are doing a lot of unnecessary things here, including that entire loop.
For example:
N = 100;
n=1; %this value is never used
phi(1)=1; % this is overwritten in loop
for n=1:N
phi(n)= 0.3*(n/N);
... (loop continues)
You don't need a loop here. Instead, work on whole vectors
N = 100;
n = 1:100; %predefine vector
phi = 0.3*(n/N); % outputs vector of phi from 0.003 to 0.3
For cases when you are combining multiple vectors remember to use ./ and .* for element-wise divison and multiplication, e.g. the last equation will end up being:
vp=sqrt((k_s+(4/3)*miu_s)./den1);