[Scilab-users] extracting elements of a matrix

[Samuel Gougeon]

Le 23/01/2016 22:17, Samuel Gougeon a écrit :
> Le 23/01/2016 17:43, fujimoto2005 a écrit :
>> Let X be a m×n matrix and f(i) is a column index for the ith row.
>> I want to get a m×1 vector y where y(i)=X(i,f(i)) for 1<=i<=m.
>> Is there any method to get y other than  the following code?
>> for i=1:m
>>     y(i)=X(i,f(i));
>> end
> Yes:
> y = X((f-1)*m+i)
with i = 1:m. So:

y = X((f-1)*m + 1:m)

Example:
--> m = 7; n = 5;
--> // X = grand(m, n,"uin", 0, 9)
  X  = [
     2.    5.    9.    9.    0.
     2.    8.    0.    3.    1.
     4.    3.    9.    9.    2.
     5.    5.    4.    6.    9.
     4.    5.    7.    6.    9.
     1.    0.    6.    6.    8.
     9.    6.    9.    3.    6.
  ]
-->i = 1:m
  i  =
     1.    2.    3.    4.    5.    6.    7.

-->// f = grand(1, m,"uin", 1, n)

  f  = [    1.    4.    4.    3.    4.    5.    2.  ]

-->X((f-1)*7+i)
  ans  =

     2.
     3.
     9.
     4.
     6.
     8.
     6.

SG