CODEWITHSUNDEEP
matlabmatrixrangeelementpi
user48540
user48540

Reputation: 41

How do I select individual elements of a given (very large) matrix, see if they are in a particular range and change them in Matlab?

I have a matrix which is 256x938. I need to go through each individual element, see if it is in the range -pi < element < pi, if it is not then we need to subtract or add a multiple of 2*pi to get the element in the range. Preferrably without for loops as we have found that they are very inefficient.

Upvotes: 4

Views: 103

Answers (3)

user85109
user85109

Reputation:

Not unlike the other solutions posed, but a bit cleaner since it requires only one simple line of code...

B = mod(A+pi,2*pi) - pi;

A = -20:2:20;
mod(A+pi,2*pi) - pi
ans =
  Columns 1 through 12
 -1.1504  0.84956 2.8496 -1.4336  0.56637 2.5664 -1.7168  0.28319 2.2832   -2   0  2

  Columns 13 through 21
 -2.2832 -0.28319 1.7168 -2.5664 -0.56637 1.4336 -2.8496 -0.84956 1.1504

Upvotes: 4

R. Schifini
R. Schifini

Reputation: 9313

I don't have Matlab at hand right now, so my suggestion might not work, but I hope the idea will.

Try something along this way:

c = cos(B); % will set all your elements between [-1 1]
B2 = acos(c);  % will return values between [0 PI] but for some the sign will be wrong
B2 = B2.*sign(sin(B)); % should set the correct sign for each element.

Hope this works.

I could have condensed all three lines to 1, but I tried to make the idea as clear as possible.

Upvotes: 0

Bitwise
Bitwise

Reputation: 7805

Is this what you want?

B=rem(A,2*pi)
B(A<-pi)=A(A<-pi)+2*pi
B(A>pi)=A(A>pi)-2*pi

Every element b in B is now -pi <= b <= pi.

It can not become -pi < b < pi as asked for in the question.

Upvotes: 1

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