Re: [R] Problems with crossprod

Spencer Graves Fri, 17 Oct 2003 02:24:03 -0700

I still have R 1.7.1, and the problem appears there as well:

> a <- A[i, ] ; crossprod(a)
             [,1]          [,2]          [,3]          [,4]          [,5]
[1,] 1.195616e-301 7.042305e-302 9.563047e-302 2.281448e-302 2.198017e-302
[2,] 6.905419e-302 1.204915e-301 3.382433e-302 2.398701e-302 2.358828e-302
[3,] 1.194968e-301 7.039991e-302 1.384628e-302 2.446584e-302 4.507199e-302
[4,] 7.046400e-302 1.204416e-301 2.444003e-302 2.357136e-302 2.446228e-302
[5,] 1.205363e-301 1.204367e-301 2.445605e-302 3.979963e-302 7.861951e-302
> a <- A[i, ] ; crossprod(a)
    [,1] [,2] [,3] [,4] [,5]
[1,]    0    0    0    0    0
[2,]    0    0    0    0    0
[3,]    0    0    0    0    0
[4,]    0    0    0    0    0
[5,]    0    0    0    0    0
> a <- A[i, ] ; crossprod(a)
    [,1] [,2] [,3] [,4] [,5]
[1,]    0    0    0    0    0
[2,]    0    0    0    0    0
[3,]    0    0    0    0    0
[4,]    0    0    0    0    0
[5,]    0    0    0    0    0
> a <- A[i, ] ; crossprod(a)
    [,1] [,2] [,3] [,4] [,5]
[1,]    0    0    0    0    0
[2,]    0    0    0    0    0
[3,]    0    0    0    0    0
[4,]    0    0    0    0    0
[5,]    0    0    0    0    0
> a <- A[i, ] ; crossprod(a)
    [,1] [,2]          [,3]          [,4] [,5]
[1,]    0    0 5.092790e-313 4.372522e-111    0
[2,]    0    0 5.708624e-307  0.000000e+00    0
[3,]  NaN    0 4.516565e-300  0.000000e+00    0
[4,]    0    0 8.997262e-312  0.000000e+00    0
[5,]    0    0 1.086462e-311  0.000000e+00    0
>
hope this helps.  spencer graves

Giovanni Marchetti wrote:

Dear R-users,

I found a strange problem working with products of two matrices, say:

a <- A[i, ] ; crossprod(a)

where i is a set of integers selecting rows. When i is empty the result is in a sense random.

After some trials the right answer (a matrix of zeros) appears.
--------------- Illustration --------------------
R : Copyright 2003, The R Development Core Team
Version 1.8.0  (2003-10-08)
A <-matrix(0, 5, 5) i <- c() a <- A[i, ] ; crossprod(a)

[,1] [,2] [,3] [,4] [,5] [1,] 6.578187e-313 NaN NaN NaN NaN [2,] NaN 1.273197e-313 NaN 1.485397e-313 NaN [3,] NaN 4.243992e-313 2.121996e-314 NaN NaN [4,] NaN 1.697597e-313 NaN 4.880590e-313 NaN [5,] 5.941588e-313 NaN NaN 1.697597e-313 NaN

a <- A[i, ] ; crossprod(a)

[,1] [,2] [,3] [,4] [,5] [1,] 2.121996e-314 5.729389e-313 NaN NaN NaN [2,] NaN NaN NaN NaN 1.909796e-313 [3,] 2.970794e-313 NaN NaN NaN NaN [4,] NaN NaN NaN 8.487983e-314 NaN [5,] NaN 6.365987e-313 2.546395e-313 NaN NaN

a <- A[i, ] ; crossprod(a)

[,1] [,2] [,3] [,4] [,5] [1,] NaN 1.485397e-313 NaN NaN 2.970794e-313 [2,] 3.182994e-313 NaN NaN 1.060998e-313 NaN [3,] NaN NaN NaN 1.697597e-313 2.737375e-312 [4,] NaN NaN NaN NaN 2.048394e+10 [5,] NaN NaN NaN NaN 2.970794e-313

a <- A[i, ] ; crossprod(a)

[,1] [,2] [,3] [,4] [,5] [1,] 1.591383e-266 20489834629 0 0 0 [2,] 5.031994e-266 0 0 0 0 [3,] 1.591205e-266 0 0 0 0 [4,] 1.264128e-267 0 0 0 0 [5,] 1.037656e-311 0 0 0 0

a <- A[i, ] ; crossprod(a)
    [,1] [,2] [,3] [,4] [,5]
[1,]    0    0    0    0    0
[2,]    0    0    0    0    0
[3,]    0    0    0    0    0
[4,]    0    0    0    0    0
[5,]    0    0    0    0    0
--------------- End of illustration------------
The same problem does not appear using the matrix product:

a <- A[i, ] ; t(a) %*% a
    [,1] [,2] [,3] [,4] [,5]
[1,]    0    0    0    0    0
[2,]    0    0    0    0    0
[3,]    0    0    0    0    0
[4,]    0    0    0    0    0
[5,]    0    0    0    0    0
Note that Splus 6 returns an error message:

a <- A[i, ] ; crossprod(a)

Problem in .Fortran.ok.Internal(if(cmplx) "zcrossp1"..: subroutine dcrossp1: Argument 1 has zero length

Thank you,

Giovanni

______________________________________________ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help


______________________________________________
[EMAIL PROTECTED] mailing list
https://www.stat.math.ethz.ch/mailman/listinfo/r-help

Re: [R] Problems with crossprod

Reply via email to