[R] package expm: matrix powers within a product of matrices: operation precedence
Rainer Sachs
sachs at math.berkeley.edu
Mon Jun 17 22:20:23 CEST 2013
package expm: matrix powers within a product of matrices: operation
precedence
I want to double check that for M and N kxk mtrices and v a k-vector
M%^%2%*%N%*%v is not automatically read as (M%^%2)%*%N%*%v or
M%*%N%^%2%*%v is not automatically read as M%*%(N%^%2)%*%v or
both
I had been assuming the usual precedence (powers first, then
multiplication) applies for matrix powers and multiplication in expm. I was
getting unexpected results. In desperation I tried putting in the
parentheses and seem to be getting much more reasonable answers. But I am so
surprised that the matrix power operation is, apparently, not automatically
given precedence over the matrix multiplication operation that I do not
trust that adding parentheses has cured my bug. Maybe I am still making some
other mistake instead. Can anyone confirm that in fact the parentheses are
(sometimes?) essential? I could not find any documentation, one way or the
other, just definitions of the power operator and of matrix exponentials.
TIA Rainer K. Sachs, Prof emertitus of math
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