[Rcpp-devel] a variable for loop
Serguei Sokol
serguei.sokol at gmail.com
Wed Dec 14 10:29:43 CET 2016
Hi Amina,
Looks like you want us to do your homework, right? ;)
Pay attention to subscript translation from R to C:
c[i-1, j, k-1] * b[i, j]
vs
c(i-1, j, k) *b(i, j)
Can you see the difference?
Best,
Serguei.
Le 14/12/2016 à 07:46, Amina Shahzadi a écrit :
> Oh sorry. No. of columns in b and size of a must always be same.
> I have made an r code to show the output.
>
>
> a = c(1, 2, 3)
> b = matrix(1:30, nrow=10, ncol=3)
> c = array(as.double(0), dim=c(10, 3, 10))
> for(i in 1:10){
> for(j in 1:3){
> for(k in 1:i){
> if(k==1) c[i, j, k] = b[i, j]
> else c[i, j, k] = c[i-1, j, k-1] * b[i, j]
> }
> }
> }
>
> Output:
>
>> c , , 1
>
> [,1] [,2] [,3]
> [1,] 1 11 21
> [2,] 2 12 22
> [3,] 3 13 23
> [4,] 4 14 24
> [5,] 5 15 25
> [6,] 6 16 26
> [7,] 7 17 27
> [8,] 8 18 28
> [9,] 9 19 29
> [10,] 10 20 30
>
> , , 2
>
> [,1] [,2] [,3]
> [1,] 0 0 0
> [2,] 2 132 462
> [3,] 6 156 506
> [4,] 12 182 552
> [5,] 20 210 600
> [6,] 30 240 650
> [7,] 42 272 702
> [8,] 56 306 756
> [9,] 72 342 812
> [10,] 90 380 870
>
> , , 3
>
> [,1] [,2] [,3]
> [1,] 0 0 0
> [2,] 0 0 0
> [3,] 6 1716 10626
> [4,] 24 2184 12144
> [5,] 60 2730 13800
> [6,] 120 3360 15600
> [7,] 210 4080 17550
> [8,] 336 4896 19656
> [9,] 504 5814 21924
> [10,] 720 6840 24360
>
> , , 4
>
> [,1] [,2] [,3]
> [1,] 0 0 0
> [2,] 0 0 0
> [3,] 0 0 0
> [4,] 24 24024 255024
> [5,] 120 32760 303600
> [6,] 360 43680 358800
> [7,] 840 57120 421200
> [8,] 1680 73440 491400
> [9,] 3024 93024 570024
> [10,] 5040 116280 657720
>
> , , 5
>
> [,1] [,2] [,3]
> [1,] 0 0 0
> [2,] 0 0 0
> [3,] 0 0 0
> [4,] 0 0 0
> [5,] 120 360360 6375600
> [6,] 720 524160 7893600
> [7,] 2520 742560 9687600
> [8,] 6720 1028160 11793600
> [9,] 15120 1395360 14250600
> [10,] 30240 1860480 17100720
>
> , , 6
>
> [,1] [,2] [,3]
> [1,] 0 0 0
> [2,] 0 0 0
> [3,] 0 0 0
> [4,] 0 0 0
> [5,] 0 0 0
> [6,] 720 5765760 165765600
> [7,] 5040 8910720 213127200
> [8,] 20160 13366080 271252800
> [9,] 60480 19535040 342014400
> [10,] 151200 27907200 427518000
>
> , , 7
>
> [,1] [,2] [,3]
> [1,] 0 0 0
> [2,] 0 0 0
> [3,] 0 0 0
> [4,] 0 0 0
> [5,] 0 0 0
> [6,] 0 0 0
> [7,] 5040 98017920 4475671200
> [8,] 40320 160392960 5967561600
> [9,] 181440 253955520 7866331200
> [10,] 604800 390700800 10260432000
>
> , , 8
>
> [,1] [,2] [,3]
> [1,] 0 0 0
> [2,] 0 0 0
> [3,] 0 0 0
> [4,] 0 0 0
> [5,] 0 0 0
> [6,] 0 0 0
> [7,] 0 0 0
> [8,] 40320 1764322560 125318793600
> [9,] 362880 3047466240 173059286400
> [10,] 1814400 5079110400 235989936000
>
> , , 9
>
> [,1] [,2] [,3]
> [1,] 0 0 0.000000e+00
> [2,] 0 0 0.000000e+00
> [3,] 0 0 0.000000e+00
> [4,] 0 0 0.000000e+00
> [5,] 0 0 0.000000e+00
> [6,] 0 0 0.000000e+00
> [7,] 0 0 0.000000e+00
> [8,] 0 0 0.000000e+00
> [9,] 362880 33522128640 3.634245e+12
> [10,] 3628800 60949324800 5.191779e+12
>
> , , 10
>
> [,1] [,2] [,3]
> [1,] 0 0 0.000000e+00
> [2,] 0 0 0.000000e+00
> [3,] 0 0 0.000000e+00
> [4,] 0 0 0.000000e+00
> [5,] 0 0 0.000000e+00
> [6,] 0 0 0.000000e+00
> [7,] 0 0 0.000000e+00
> [8,] 0 0 0.000000e+00
> [9,] 0 0 0.000000e+00
> [10,] 3628800 670442572800 1.090274e+14
>
>
>
>
> On Wed, Dec 14, 2016 at 7:27 PM, Avraham Adler <avraham.adler at gmail.com <mailto:avraham.adler at gmail.com>> wrote:
>
>
>
> On Wed, Dec 14, 2016 at 1:24 AM Amina Shahzadi <aminashahzadi at gmail.com <mailto:aminashahzadi at gmail.com>> wrote:
>
> Hello Avraham --Happy to see you
>
> My code is trying to produce a cube c which is going to be constructed by a vector a and matrix b.
> And the number of rows in b and size of a must be same.
>
> So we can assume that if a is a vector of size 3, Then b must be 2 x 3 or 3 X 3 etc.
>
> Thank you Avraham for quick response. I hope this will make my question more clear.
>
> Best regards
>
>
> On Wed, Dec 14, 2016 at 4:46 PM, Avraham Adler <avraham.adler at gmail.com <mailto:avraham.adler at gmail.com>> wrote:
>
> On Tue, Dec 13, 2016 at 9:51 PM, Amina Shahzadi <aminashahzadi at gmail.com <mailto:aminashahzadi at gmail.com>> wrote:
>
> Hello Friends and Prof. Dirk
>
> I am pasting here a code which has a for loop depending on another for loop.
> I am getting zeros for cube c. I tried and searched a lot but did not get an example of this type. Would you please help in this regard?
>
>
> #include <RcppArmadillo.h>
> using namespace Rcpp;
> using namespace RcppArmadillo;
> using namespace arma;
> //[[Rcpp::depends(RcppArmadillo)]]
> //[[Rcpp::export]]
>
>
> arma::cube exam(arma::vec a, arma::mat b)
> {
> int m = a.size();
> int n = b.n_rows;
> arma::cube c = zeros<cube>(n, m, n);
> for(int i=0; i<n; i++) {
> for(int j=0; j<m; j++) {
> for(int k=0; k<i; k++) {
> if(k==0) {
> c(i, j ,k) = c(i, j, k) + b(i, j);
> }
> else{
> c(i, j, k) = c(i, j, k) + c(i-1, j, k) *b(i, j);
> }
> }
> }
> }
> return c;
> }
>
>
> Thank You
> --
> /Amina Shahzadi/
>
>
>
>
> Hello.
>
> I haven't run your code, but it strikes me
>
> that I cannot see where are you capturing the number of columns of b.
>
> It's a bit confusing as I was always taught a matrix has m rows and n
>
> columns. Be that as it may, your k==0 loop looks like it's trying to
>
> copy over the original matrix to the first slice, but how do you know
>
> that b has m columns, which is what you're assuming by letting j loop to
>
> m. Unless you are assuming a square matrix?
>
> Even if you are, if your matrix is not the same length as your vector, I think there is an issue with your loop boundaries, unless I've
> misunderstood something, which is certainly possible.
>
> For example, assume a is {1, 2, 3} and b is the 2 x 2 of row 1: [1 2] and row 2: [3 4]. Thus m = 3 and n = 2.
>
> Step 1: i = j = k = 0: c(0, 0, 0) becomes b(0, 0) or 1.
>
> Step 2: i = 0, j = 1, k = 0: c(0, 1, 0) becomes b(0, 1) or 2.
>
> Step 3: i = 0, j = 2, k = 0: c(0, 2, 0) becomes b(0, 2) ?!?! There is no b(0, 2), it's only a 2x2 matrix?
>
>
> Similar to your previous questions, instead of posting code, can you please describe in words what it is you are trying to do? That may help.
>
> Avi
>
>
>
>
>
>
> --
> /Amina Shahzadi/
>
>
> Constructed how? Can you provide a simple set of inputs and the expected output?
>
> Avi
> --
> Sent from Gmail Mobile
>
>
>
>
> --
> /Amina Shahzadi/
>
>
> _______________________________________________
> Rcpp-devel mailing list
> Rcpp-devel at lists.r-forge.r-project.org
> https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-devel
>
More information about the Rcpp-devel
mailing list