help please why ??

A = [ 1 3 2 6 ; 5 7 7 0 ; -2 6 -2 1 ] ;

j = sum(A(1))

j= 1 why ???

Answer 1

[Jim Riggs]

the statement

 sum(A(1))

is summing only the first element in A, which is 1.

If you want to sum the first row, it should be

 sum(A(1,:))

and if you want to sum the first column, it is

 sum (A(:,1))

[ahmad qadan]

thx but the first element is 1 ,, 1+1 = 2 i cant understand it

[Jim Riggs]

The matrix A is:

    1   3   2  6
    5   7   7  0
   -2   6  -2  1

The first element in A is A(1) which is 1. So the statement

 sum(A(1))

is the same as

 sum(1)

and has a value of 1.

[ahmad qadan]

oooohhh ok thx a lot

Answer 2

[elham kreem]

WHAT are you want? IF YOU want to sum all the values then use Sum (A) BUt you sum the first element only. IF you help this answer then except to it.

[ahmad qadan]

why j = 1 ,, if the sum first element 1+1 = 2