Matlab : Creating an array of a single value

Question

Hey,

I'm using matlab and want to check whether a column vector is equal to another withing 3dp, to do this i'm trying to create an array full of 0.001 and checking whether it is greater than or equal. is there a simpler way than a for loop to create this array or no?

if more info is needed just ask, i'm not very good at this.

Cheers, Andrew

Answer 1

You may consider the 'find' command, like:

a = [ 0.005, -0.003 ];
x = find(a > 0.001);

FWIW, I've found comparing numbers in MATLAB to be an absolute nightmare, but I am also only new to it. The point is, you may have floating-point comparision issues when do you the compares, so keep this in mind when attempting anything (and someone please correct me if I'm wrong on this or there is a beautiful workaround.)

Answer 2

Example:

a = rand(1000,1);
b = rand(1000,1);

idx = ( abs(a-b) < 0.001 );
[a(idx) b(idx)]

» ans =
       0.2377      0.23804
       0.0563     0.056611
      0.01122     0.011637
        0.676       0.6765
      0.61372      0.61274
      0.87062      0.87125

Answer 3

So, let me know if this is correct.

You have 2 vectors, a and b, each with N elements. You want to check if, for each i<=N, abs(a(i)-b(i)) <= 0.001.

If this is correct, you want:

vector_match = all(abs(a-b) <= 0.001);

vector_match is a boolean.

Answer 4

is there a simpler way than a for loop to create this array or no?

Yes, use

ones(size, 1) * myValue

For instance

>> ones(5,1)*123

ans =

   123
   123
   123
   123
   123