Meaning of : in the parentheses

jasoncurious

Hi guys, I am currently doing a Matlab program for partial pivoting. I looked at my friend's example:

Code:

% Partial Pivoting
for i=1:n-1
for j = i+1:n
if (a(j,i)) > (a(i,i))
u=a(i,:);
a(i,:)=a(j,:);
a(j,:)=u;
v=b(i,1);
b(i,1)=b(j,1);
b(j,1)=v;
end
end
end

I was wondering what's the meaning of the : in the parentheses. Is it some sort of Matlab keyword? Thanks for helping

Simon Bridge

The colon stands for a whole line in the matrix. Observe:

Code:

octave:117> m=magic(4)
m =

   16    2    3   13
    5   11   10    8
    9    7    6   12
    4   14   15    1

octave:118> m(2,:)
ans =

    5   11   10    8

octave:119> m(:,2)
ans =

    2
   11
    7
   14

... see?
... so m(2,:) says to take the entire second row while the m(:,2) says take the second column.
http://volga.eng.yale.edu/sohrab/mat...colon_operator
(Matlab works the same way...)

jasoncurious

Thanks bro.

Simon Bridge

No worries ;)
Generally, you can try out the confusing operations you see on some random matrix and see what happens ... the magic-square function is very useful for this.

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Simon Bridge Recognitions: Homework Help	The colon stands for a whole line in the matrix. Observe: Code: octave:117> m=magic(4) m = 16 2 3 13 5 11 10 8 9 7 6 12 4 14 15 1 octave:118> m(2,:) ans = 5 11 10 8 octave:119> m(:,2) ans = 2 11 7 14 ... see? ... so m(2,:) says to take the entire second row while the m(:,2) says take the second column. http://volga.eng.yale.edu/sohrab/mat...colon_operator (Matlab works the same way...)

Simon Bridge Recognitions: Homework Help	Meaning of : in the parentheses No worries ;) Generally, you can try out the confusing operations you see on some random matrix and see what happens ... the magic-square function is very useful for this.