[R] package expm: matrix powers within a product of matrices: operation precedence

Rainer K. SACHS rainersachs at berkeley.edu
Tue Jun 18 00:08:38 CEST 2013

Thanks, that clears everything up completely. It might be worth adding
your comment to the available documentation.

On 6/17/13, William Dunlap <wdunlap at tibco.com> wrote:
> All operators of the form %<something>% have the same precedence,
> that of %*%.    R does not look at the <something> between the percent
> signs to determine the precedence.  Hence you must use parentheses
> to get the order of operations that you want.
> (I think that %<something>% operators are overused - providing the same
> functionality in a standard functional form is often more convenient.  It
> certainly would eliminate your problem.)
> Bill Dunlap
> Spotfire, TIBCO Software
> wdunlap tibco.com
>> -----Original Message-----
>> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
>> On Behalf
>> Of Rainer Sachs
>> Sent: Monday, June 17, 2013 1:20 PM
>> To: r-help at r-project.org
>> Subject: [R] package expm: matrix powers within a product of matrices:
>> operation
>> precedence
>> 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
>> --
>> View this message in context:
>> http://r.789695.n4.nabble.com/package-expm-matrix-
>> powers-within-a-product-of-matrices-operation-precedence-tp4669733.html
>> Sent from the R help mailing list archive at Nabble.com.
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