# [R] Matrix element-by-element multiplication

R. Michael Weylandt michael.weylandt at gmail.com
Sun Nov 6 05:21:34 CET 2011

```There are a few (nasty?) side-effects to c(), one of which is
stripping a matrix of its dimensionality. E.g.,

x <- matrix(1:4, 2)
c(x)
[1] 1 2 3 4

So that's probably what happened to you. R has a somewhat odd feature
of not really considering a pure vector as a column or row vector but
being willing to change it to either:

e.g.

y <- 1:2

x %*% y
y %*% x
y %*% y

while matrix(y) %*% x throws an error, which can also trip folks up.
You might also note that x * y and y*x return the same thing in this
problem.

Getting back to your problem: what are v and b and what are you hoping
to get done? Specifically, what happened when you tried v*b (give the
exact error message). It seems likely that they are non-conformable
matrices, but here non-conformable for element-wise multiplication
doesn't mean the same thing as it does for matrix multiplication.
E.g.,

x <- matrix(1:4,2)
y <- matrix(1:6,2)

dim(x)
[1] 2 2

dim(y)
[1] 2 3

x * y -- here R seems to want matrices with identical dimensions, but
i can't promise that.

x %*% y does work.

Hope this helps and yes I know it can seem crazy at first, but there
really is reason behind it at the end of the tunnel,

Michael

On Sun, Nov 6, 2011 at 12:11 AM, Steven Yen <syen at utk.edu> wrote:
> My earlier attempt
>
>    dp <- v*b
>
> did not work. Then,
>
>    dp <- c(v)*b
>
> worked.
>
> Confused,
>
> Steven
>
> At 09:10 PM 11/4/2011, you wrote:
>
> Did you even try?
>
> a <- 1:3
> x <-  matrix(c(1,2,3,2,4,6,3,6,9),3)
> a*x
>
>      [,1] [,2] [,3]
> [1,]    1    2    3
> [2,]    4    8   12
> [3,]    9   18   27
>
> Michael
>
> On Fri, Nov 4, 2011 at 7:26 PM, Steven Yen <syen at utk.edu> wrote:
>> is there a way to do element-by-element multiplication as in Gauss
>> and MATLAB, as shown below? Thanks.
>>
>> ---
>> a
>>
>>        1.0000000
>>        2.0000000
>>        3.0000000
>> x
>>
>>        1.0000000        2.0000000        3.0000000
>>        2.0000000        4.0000000        6.0000000
>>        3.0000000        6.0000000        9.0000000
>> a.*x
>>
>>        1.0000000        2.0000000        3.0000000
>>        4.0000000        8.0000000        12.000000
>>        9.0000000        18.000000        27.000000
>>
>>
>> --
>> Steven T. Yen, Professor of Agricultural Economics
>> The University of Tennessee
>> http://web.utk.edu/~syen/
>>        [[alternative HTML version deleted]]
>>
>> ______________________________________________
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