How can I increase the number of digits displayed when using Armadillo library

Question

I am using the Armadillo linear algebra library to diagonalize matrices. I need to increase the number of digits displayed/written to a file at the end. According to Armadillo's reference, "arma::mat" will create a double matrix. So, I tried using std::setprecision from "iomanip", but it did not quite work. Here is a minimal code that captures the problem:

#include<iostream>
#include<armadillo>
#include<iomanip>

int main()
{
   double Trace_A = 0.;
   arma::mat A;
   A = :arma::randu<arma::mat>(5,5);
   Trace = arma::trace(A);         

   // Normal output
   std::cout << "A = \n" <<A ;
   std::cout << "Trace(A) = " << Trace_A << std::endl;
   std::cout << "---------------------------------------------" << std::endl;

   // Displaying more digits
   std::cout << std::fixed << std::setprecision(15);
   std::cout << "A = \n" << A;
   std::cout << "Trace(A) = " << Trace_A << std::endl;
}

And, here is what I get:

A = 
   0.8402   0.1976   0.4774   0.9162   0.0163
   0.3944   0.3352   0.6289   0.6357   0.2429
   0.7831   0.7682   0.3648   0.7173   0.1372
   0.7984   0.2778   0.5134   0.1416   0.8042
   0.9116   0.5540   0.9522   0.6070   0.1567
Trace(A) = 1.83848
---------------------------------------------
A = 
   0.8402   0.1976   0.4774   0.9162   0.0163
   0.3944   0.3352   0.6289   0.6357   0.2429
   0.7831   0.7682   0.3648   0.7173   0.1372
   0.7984   0.2778   0.5134   0.1416   0.8042
   0.9116   0.5540   0.9522   0.6070   0.1567
Trace(A) = 1.838476590271330

Curiously, it works for the trace which is passed on to the double variable "Trace_A" but not for the matrix itself. Any idea what I am doing wrong here?

Nothing. Presumably the lib itself `setprecision`s the stream before printing. — The Paramagnetic Croissant, Nov 08 '14 at 16:46

score 6 · Answer 1 · answered Nov 08 '14 at 20:16

I think I figured out how to do this. It can be done using "raw_print":

A.raw_print(std::cout);

This gives:

0.8402   0.1976   0.4774   0.9162   0.0163
0.3944   0.3352   0.6289   0.6357   0.2429
0.7831   0.7682   0.3648   0.7173   0.1372
0.7984   0.2778   0.5134   0.1416   0.8042
0.9116   0.5540   0.9522   0.6070   0.1567

0.84018771715 0.19755136929 0.47739705186 0.91619506800 0.01630057162
0.39438292682 0.33522275571 0.62887092476 0.63571172796 0.24288677063
0.78309922376 0.76822959481 0.36478447279 0.71729692943 0.13723157679
0.79844003348 0.27777471080 0.51340091020 0.14160255536 0.80417675423
0.91164735794 0.55396995580 0.95222972517 0.60696887626 0.15667908925

score 1 · Answer 2 · answered Jun 27 '20 at 18:56

Following is one of the ways to set precision before using raw_print

arma::mat A = arma::randu<arma::mat>(5,5);

cout.precision(11);
cout.setf(ios::fixed);

A.raw_print(cout, "A:");

Normal of setting precision also works

arma::mat A = arma::randu<arma::mat>(5,5);

cout << fixed << setprecision(11);

A.raw_print(cout, "A:");

How can I increase the number of digits displayed when using Armadillo library

2 Answers2