Converting code from MATLAB to R

Question

I'm trying to convert some code from MATLAB to R.

I'm having particular problems converting this part of a differential equation:

In MATLAB :

dA.*(A*N - N.*sum(A,2))

where dA is an integer, A is a 10x10 matrix and N is a 10x1 matrix (see example code below)

In R so far I've got this:

dA*(A*N - N*colSums(A))

but for some reason it doesn't seem to be giving the same result. Does anyone have any ideas as to what I've done wrong?

Example of the data I'm using below:

in MATLAB:

dA = 0.1;
N = 120000*ones(1,nN);
seq = [0 1 0 0 0 1 0];
seq2 = repmat(seq,1,20);
seq100 = seq2(1:100) 
A = AA-diag(diag(AA));

in R:

dA <- 0.1                          
N <- c(120000, 120000, 120000, 120000, 120000, 120000, 120000, 120000, 120000, 120000)
num_zeros_int <- zeros(70, 1)
num_ones_int <- ones(30, 1)
seq <- c(0,1,0,0,0,1,0)
seq2<- rep(seq, times = 20)
seq100 <- seq2[0:100]
int_mat <- matrix(seq100, nests, nests)

Well, `*` and `.*` are different mathemathical operations in MATLAB, however you are translating both of them as `*` to R, so I assume that is the problem. Also, your matrix is random, so I hope it always gives a different result! else you broken randomenss. — Ander Biguri, May 08 '17 at 09:43
This might help: http://mathesaurus.sourceforge.net/octave-r.html — coffeinjunky, May 08 '17 at 09:44
@AnderBiguri Thanks! I'll have a look at that. Ah yes, sorry I should have included my non-random data that I was testing it on - I'll change that now. — unknown, May 08 '17 at 09:47

score 1 · Accepted Answer · answered May 08 '17 at 13:32

Matlab expression:

dA.*(A*N - N.*sum(A,2))

where

dA: real number
A: 10 x 10 matrix
N: 10 X 1 matrix
A*N: matrix multiplication
sum(A,2): sum of rows in A (10x1 matrix)
N.*sum(A,2): element by element multiplication (10 x 1 matrix)

Let's set up the following example in R:

A = matrix(data = 1:100,nrow = 10)
N = matrix(data = 1:10)
dA = 0.1

> A
      [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
 [1,]    1   11   21   31   41   51   61   71   81    91
 [2,]    2   12   22   32   42   52   62   72   82    92
 [3,]    3   13   23   33   43   53   63   73   83    93
 [4,]    4   14   24   34   44   54   64   74   84    94
 [5,]    5   15   25   35   45   55   65   75   85    95
 [6,]    6   16   26   36   46   56   66   76   86    96
 [7,]    7   17   27   37   47   57   67   77   87    97
 [8,]    8   18   28   38   48   58   68   78   88    98
 [9,]    9   19   29   39   49   59   69   79   89    99
[10,]   10   20   30   40   50   60   70   80   90   100

> N
      [,1]
 [1,]    1
 [2,]    2
 [3,]    3
 [4,]    4
 [5,]    5
 [6,]    6
 [7,]    7
 [8,]    8
 [9,]    9
[10,]   10

The first term is:

z1 = A %*% N

And the second term:

srow = rowSums(A)
z2 = srow * N

Which leads to the final result:

result = dA * (z1-z2)

Final equation

result = dA * (A %*% N - rowSums(A)*N)

This should give you the same answer as Matlab's dA.*(A*N - N.*sum(A,2))

Converting code from MATLAB to R

1 Answers1