On 27/09/2017 8:47 PM, Evan Cooch wrote:
Suppose I have interest in a matrix with the following symbolic
structure (specified by 3 parameters: sa, so, m):
matrix(c(0,sa*m,so,sa),2,2,byrow=T)
What I can't figure out is how to construct a series of matrices, where
the elements/parameters are rnorm values. I'd like to construct separate
matrices, with each matrix in the series using the 'next random
parameter value'. While the following works (for generating, say, 5 such
random matrices)
replicate(5,matrix(c(0,rnorm(1,0.8,0.1)*rnorm(1,1.2,0.1),rnorm(1,0.5,0.1),rnorm(1,0.8,0.1)),2,2,byrow=T))
its inelegant, and a real pain if the matrix gets large (say, 20 x 20).
I'm wondering if there is an easier way. I tried
> sa <- rnorm(5,0.8,0.1)
> so <- rnorm(5,0.5,0.1)
> m <- rnorm(5,1.2,0.1)
matrix(c(0,sa*m,so,sa),2,2,byrow=T)
but that only returns a single matrix, not 5 matrices as I'd like. I
also tried several variants of the 'replicate' approach (above), but
didn't stumble across anything that seemed to work.
So, is there a better way than something like:
replicate(5,matrix(c(0,rnorm(1,0.8,0.1)*rnorm(1,1.2,0.1),rnorm(1,0.5,0.1),rnorm(1,0.8,0.1)),2,2,byrow=T))
Peter's mapply solution is probably the best. Another that might be a
little faster (but more obscure) is to use a 3-index array. I think
this is what you'd want, with sa, so, and m as defined above:
ms <- array(c(rep(0, 5),sa*m,so,sa), c(5, 2, 2))
Then matrix i will be stored as ms[i,,].
Duncan Murdoch
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