[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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