CODEWITHSUNDEEP
c++eigenfunction-definition
Ema
Ema

Reputation: 79

Decimal points are not stored as expected when Eigen library is used in function definition

I am doing a C++ program using Eigen library and when I executed my code I got my variable P as 

`-4 -3 -2 -1 0 1 2 3 4 5`

But it should be -4.5 -3.5-2.5-1.5-0.5 1.5 2.5 3.5 4.5 The numbers are getting rounded to the nearest integers towards infinity.Please help me find a solution to my problem.

#include<iostream>
#include<math.h>
#include<stdlib.h>
#include<eigen3/Eigen/Dense>
#include<eigen3/Eigen/Core>
using namespace Eigen;
using namespace std;
using Eigen::MatrixXd;
using Eigen::MatrixXf;

MatrixXf create_linear_array(int &N1 , double &dx)
{


int i;MatrixXf num(10,1);
    for(i=0;i<10;i++)
     num(i,0)=(float)(((i+1)-(N1+1)/2));
return num;
}

int main()
{
//---------------------INITIALISATION & DECLARATION------------------------------

    double dx=0.030;
    int N1=10;

    MatrixXf P;
    P=create_linear_array(N1,dx);

    cout<<P<<endl;
    return 0;


}

Upvotes: 0

Views: 431

Answers (2)

chtz
chtz

Reputation: 18827

The cause of your error was already pointed out by @john. I just want to point out that there is a built-in function LinSpaced in Eigen for what you want to do:

int N1=10;

MatrixXf P;  // consider using VectorXf here
float const limit = 0.5f*(N1-1);
P = VectorXf::LinSpaced(N1, -limit, +limit);

Upvotes: 2

john
john

Reputation: 87932

You are doing integer division and the result of integer division is always an integer. Only afterwards do you cast the result to a float, but then it is too late. Simplest way to fix this is to use a floating point literal 2.0 instead of 2. This works because 2.0 is a double and when you divide an integer by a double, the integer is converted to a double first.

num(i,0)=(float)(((i+1)-(N1+1)/2.0));

Upvotes: 3

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