Register to reply

Meaning of : in the parentheses

by jasoncurious
Tags: meaning, parentheses
Share this thread:
jasoncurious
#1
Dec7-12, 04:37 AM
P: 8
Hi guys, I am currently doing a Matlab program for partial pivoting. I looked at my friend's example:

% 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
Phys.Org News Partner Science news on Phys.org
Guidelines for enhancing solar cells using surface plasmon polaritons
Trees and shrubs invading critical grasslands, diminish cattle production
Climate change will threaten fish by drying out Southwest US streams, research predicts
Simon Bridge
#2
Dec7-12, 05:35 AM
Homework
Sci Advisor
HW Helper
Thanks
Simon Bridge's Avatar
P: 12,739
The colon stands for a whole line in the matrix. Observe:
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
#3
Dec7-12, 06:23 AM
P: 8
Thanks bro.

Simon Bridge
#4
Dec7-12, 07:26 AM
Homework
Sci Advisor
HW Helper
Thanks
Simon Bridge's Avatar
P: 12,739
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.


Register to reply

Related Discussions
Parentheses around mismatched size fractions in LaTeX Math & Science Software 2
Order of Parentheses in a Sum Calculus & Beyond Homework 6
Sigma notation and parentheses question Calculus & Beyond Homework 7
When decimals and/or fractions are only within the parentheses in a linear equation Precalculus Mathematics Homework 4
Parentheses ... or brackets (US/UK terminology question) Precalculus Mathematics Homework 4