CODEWITHSUNDEEP
octave
TimGJ
TimGJ

Reputation: 1654

Summing a single row vector by column in Octave

I have written a short Octave script which draws the function sum(sin(2k-1)/(2k-1)) for k = 1..n terms. (I am attempting to model how successive terms make the output converge to a square wave. 

% Program to model square-wave using sum of sines

terms=3

theta=linspace(0, 6*pi, 1000);
k=[1:terms]';
n=2*k-1;

q=sin(n*theta)./n;
y=sum(q);
plot(theta, y);

It works OK (i.e. the sum() function returns a vector containing the sum of each column) for terms > 1. But when terms == 1 (i.e. it should just draw a sine wave) the sum() function computes the sum of the row and just returns a scalar.

How do I get the sum() function to total each column even if there is only one row or how do I reshape or slice or whatever the row vector such that rather than being a 1-dimensional vector of dimension n it effectively becomes a 2-dimensional matrix of dimension 1xn?

Upvotes: 0

Views: 7612

Answers (2)

carandraug
carandraug

Reputation: 13081

sum(), like many other functions in Octave, will act on the first non-singleton dimension by default. So all you need to do is to be specific about the dimension. From sum() help text:

If DIM is omitted, it defaults to the first non-singleton dimension.

So, all you need to do is be specific about the dimension, i.e., use sum (q, 1):

terms = 1

theta = linspace (0, 6*pi, 1000);
k = [1:terms]';
n = 2*k-1;

q = sin (n*theta) ./ n;
y = sum (q, 1);
plot (theta, y);

Upvotes: 8

Chmiel123
Chmiel123

Reputation: 64

q=sin(n*theta)./n;
if (terms == 1)
    y = q;
else
    y=sum(q);
end
plot(theta, y);

See if that works.

Upvotes: -1

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