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rmatrixmatrix-multiplicationexponential

R: Can I use some sort of matrix multiplication with exponentials?

I have data matrix (X) of the dimensions 5000x250 plus an extra parameter Y (Dim: 5000x1). The following loop gives me the desired results, but it takes forever to compute.

for (i in 1:ncol(X))
  for (j in 1:nrow(X))
   {
   X[j,i]=Y[j,1]^X[j,i]
   }

Is there any way to optimize this? If I didn't require the exponential, I'd use matrix multiplication. Thanks!

Solution

  • Turn your column vector y into a matrix and use elementwise ^.

    matrix(y, nrow=nrow(X), ncol=ncol(X)) ^ X

    or

    rep(y, times=ncol(X)) ^ X