MATLAB Matlab summation of a complex function

[Waxterz]

Hi,

I need to plot the last function of this:

But I don't know how to generate the sum. I know the for loop is totally wrong, but I can't go any further. This is what I have:

K = 8;
L = 950*10^-9;
g = 2*pi/L;
v0 = 30;
v = -90:10:90;
d = 950*10^-9;
for i = 1:8;

S = exp(1i*g*(K-i)*d*(sind(v)-sind(v0)));
end
A = 20*log(abs(S)/8);
A

Can someone fix the summation loop part for me?

Thanks in advance

 

[DrClaude]

You need to set S to zero before the loop, then

S = S + exp(1i*g*(K-i)*d*(sind(v)-sind(v0)));

 

[Waxterz]

You need to set S to zero before the loop, then

S = S + exp(1i*g*(K-i)*d*(sind(v)-sind(v0)));

Hi DrClaude,

I posted it on the forum, just in case I didn't found the answer myself. I knew it had something to do with setting something on zero. :)

So I tried something, I tried this:

K = 8;
L = 950*10^-9;
g = 2*pi/L;
v0 = 30;
v = -90:10:90;
d = 950*10^-9;
Ssum = 0;
for i = 1:8;
Ssum = S + Ssum;
S = exp(1i*g*(K-i)*d*(sind(v)-sind(v0)));
end
A = 20*log(abs(Ssum)/8);
AIs this equivalent to yours? Thanks for your help and quick reply, btw.

 

[Waxterz]

Yea, I'm going to do your version. Got the inner matrix dimensions degree error. Anyway thx!

 

[DrClaude]

Hi DrClaude,

I posted it on the forum, just in case I didn't found the answer myself. I knew it had something to do with setting something on zero. :)

So I tried something, I tried this:

K = 8;
L = 950*10^-9;
g = 2*pi/L;
v0 = 30;
v = -90:10:90;
d = 950*10^-9;
Ssum = 0;
for i = 1:8;
Ssum = S + Ssum;
S = exp(1i*g*(K-i)*d*(sind(v)-sind(v0)));
end
A = 20*log(abs(Ssum)/8);
AIs this equivalent to yours? Thanks for your help and quick reply, btw.

Your use of Ssum is better if you need $S_a$ afterwards. But I see a few things that could be better, and one error.

First,

for i = 1:8;

would be better as

for i = 1:K

since K is already defined. Second, since Ssum will be an array (as is S), you should initialize it as an array of zeros:

Ssum = zeros(19,1);

Finally,

Ssum = S + Ssum;
S = exp(1i*g*(K-i)*d*(sind(v)-sind(v0)));

will not work. What happens at the first and last iterations of the loop?