for instance if there is a vector or a matrix include an element 26, how can I find the position (i,j) of 26 in the vector?
I'm new for Eigen, pls give me some help, thanks

There is no equivalent. If you know there is only one, you can do:

Code: Select all

ArrayXXf A;
int i, j;
if( (A==26).maxCoeff(&i,&j) )
{
  ...
}
else  // otherwise there is no element equals to 26.
...


ggael wrote:There is no equivalent. If you know there is only one, you can do:

Code: Select all

ArrayXXf A;
int i, j;
if( (A==26).maxCoeff(&i,&j) )
{
  ...
}
else  // otherwise there is no element equals to 26.
...


dear ggael, I tried as you told me, but there is a mistake at A==26, it says: no operator "==" matches this operands.

Code: Select all

ArrayXXi A(4,4);
   A<<1,56,4,6,
      45,76,43,22,
      3,42,4,2,
      4,6,7,9;
   int i,j;
   if ((A==3).maxCoeff(&i,&j))
   {
      cout<<"Yes";
   }
   else
   {
      cout<<"No";
   }
   

Works for me. Maybe you're using an old version.

I changed my Eigen version to 3.1.3 but it still not work, could you give me some details about yours which works well.

just like:

#include <Eigen/eigen>
#include <iostream>
using namespace std;
using namespace Eigen;

int main()
{
ArrayXXi A(4,4);
A<<1,56,4,6,
45,76,43,22,
3,42,4,2,
4,6,7,9;
int i,j;
if ((A==36).maxCoeff(&i,&j))
{
cout<<"Yes";
}
else
{
cout<<"No";
}
return 0;
}

I've got it. thanks very much