# Array operations in Matlab?

by ichbinschneller
Tags: array, matlab, operations
 P: 2 Is it possible to apply operations to the rows of a matrix as an array? Such as I have a matix A which is 30 rows by 1 column and I want to treat each row as a vector such that I can solve for the polynomial roots of each row using the roots comand (treating each row as its own equation and the matrix A a system of eqautions)? Also would it be possible to take the square roots of each row of a same size matrix. Meaning say I had the same size matrix and I want to take the square root of each row and have the output be a matrix of the same size just with the values of those square roots?
 Emeritus Sci Advisor PF Gold P: 1,817 Hi, Iamfaster Welcome to PF! If you need to perform a function on each row of a matrix like function(A), where A is a 30x1 vector, I think you'll have to break it up and write a for loop for i=[1:length(A)] function(A(i)); end or if A is 30x2 (or more) for i=[1:length(A)] function(A(i,:)); end if you want to take the square root, you can find it using the .^ operator, which raises each element to a power as opposed to the ^ which performs matrix multiplication A.^(1/2)
 P: 2 Thanks, I am getting closer now but I still cant seem to enter the code in the right form. Say I have a matrix g1= 5 9 8 4 7 6 1 2 8 and I want a matrix g2= roots of each row as if each row was a vector consisting of the coeficients of a polynomial. I have tried using code such as for i=[1:length(g1)] g2(i)=roots(g1(i)); end but I keep getting errors. What am I doing wrong? What code would yield the results I desrire?
Emeritus
PF Gold
P: 1,817
Array operations in Matlab?

 Quote by ichbinschneller for i=[1:length(g1)] g2(i)=roots(g1(i)); end What am I doing wrong? What code would yield the results I desrire?
You're not indexing the entire row.

g1(1) doesn't have any meaning for a m by n matrix when n>1.

If you want to reference a single term, you need to put in the entire address lke so:

g1(1,2)

to reference the first row, second column.

If you want to reference the entire row, you need to put in the : operator like so:

g1(1,:)

Just using : by itself is "shorthand" for explicitly defining the starting and ending conditions.

If your matrix g is 4x4

g=[1,2,3,4
6,7,8,9
10,11,12,13
14,15,16,17]
typing

a=g(2,2:3) will give the result a=[7,8]
b=g(:,1) will give the result b=[1;6;10;14]
c=g(3,1:4) will give the result c=[10,11,12,13]
and
d=g(3,:) will give the same result as c. d=[10,11,12,13]

Hope that helps,
 P: 540 also, lose the [ and the ] like this: for i = 1:length(g1) g2(i, :) = roots(g1(i, :)); end
Emeritus