Making IF conditional sentance.

Hi guys. I want to make some if conditional sentance.

I can't get a result, because of 'f'.

-----------------------------------------------------

f=[0:1:20]
f1=10;
E=20;
B0=15;

if  (0<f && f<f1);

 P  =  sqrt(E)/(2*B0);

elseif (f1<f && f<2*B0-f1);         

   P  =  (sqrt(E)/(4*B0))*(1+cos((pi*(abs(f)-f1))/(2*(B0-f1))));

else 

   P  =  0

end

plot(f,2*B0*P/sqrt(E));

-----------------------------------------------------------------

Matlab says that && can't be used with doubled value..

Please help.

Answer 1

[Stephen23]

Learn how to write vectorized code in MATLAB: vectorized code is faster, neater and less buggy. Firstly we define the parameters:

>> f = 0:20;
>> f1 = 10;
>> E = 20;
>> B0 = 15;

Then a vectorized solution can be achieved by directly using logical indexing:

>> P = (sqrt(E)/(4*B0)) * (1+cos((pi*(abs(f)-f1)) / (2*(B0-f1))));
>> P(0<f & f<f1) = sqrt(E)/(2*B0);
>> P(f==0 | f==f1) = 0;
>> P(:)
ans = 
          0
    0.14907
    0.14907
    0.14907
    0.14907
    0.14907
    0.14907
    0.14907
    0.14907
    0.14907
          0
    0.14542
    0.13484
    0.11835
   0.097568
   0.074536
   0.051503
   0.030725
   0.014235
   0.003648
          0

[baek]

It really helpful. Thanks. I never thought about like this.

Now I can make a really nice signal. Thank you

Answer 2

[James Tursa]

f is a vector, so the expression f<f1 is also a vector. And when you try to use this vector with the && operator you get the error message.

Either vectorize all of this to generate your P if you are up to the task, or wrap it in a loop to generate your P values using only one element of f in each iteration to generate one element of P.

[baek]

Yes. I thought it is quite difficult to solve. But there is a solution form 'Stephen Codeldick' under below. Thanks for your mention. :D