#orca_array

Author: Pramod Gupta, Department of Astronomy, University of Washington

Last Modified: 2020 Oct 26

orca_array consists of multi-dimensional array template classes array1d to array7d with compile time options for array bounds checking and for accessing array elements via Fortran order or C order.

See orca_array.hpp for the code.

(1) Why are orca_array arrays only up to only upto 7 dimensions?

• In classical physics, to describe a particle you need 3 space coordinates (x,y,z), 3 velocities (v_x, v_y, v_z) and time t.
• More than 7 dimensional arrays are very rare since memory usage increases exponentially like L^d where L is the size of one dimension and d is the number of dimensions.
• If you need more dimensions, the array7d code can easily be modified for arrayNd.

(2) What compilers can compile orca_array.hpp?

orca_array.hpp has been compiled with g++, clang++, and icpc.

(3) How can one choose between column-major and row-major order of accessing arrays?

Choose one of below options in orca_array.hpp:

//First index changes fastest
#define FORTRAN_ORDER 1

//Last index changes fastest (C order)
#define FORTRAN_ORDER 0

(4) Can you show examples of using orca_array arrays?

#include "orca_array.hpp"
using namespace orca_array;

//defining 2D array
array2d<double> b(10,8);

//using 2D array
b.at(3,4)=3.14;

//Copy constructor and assignment operator are private.
//Hence pass all orca_arrays to a function by reference.

//passing 2D array to function
//m, n are optional
double trace(int m, int n, array2d<double> & myarray2d){
. . .
}

(5) How can one turn on or turn off array bounds checking?

Choose one of the below options in orca_array.hpp:

#define ARRAY_BOUNDS_CHECK 1

#define ARRAY_BOUNDS_CHECK 0

If ARRAY_BOUNDS_CHECK is 1 and during run time an array index is out of bounds then the program will encounter a segmentation fault.

Compile the program with the -g option and run in the debugger to identify the line of code as shown below.

Suppose a program xyz.cpp uses orca_array.hpp. If the program xyz.cpp has a bug and it runs into a segmentation fault due to array out of bounds or negative sizes of dimensions then use the below steps to identify the buggy line of code.

GNU Compiler:

g++ -g xyz.cpp -o xyz
gdb xyz
run
bt  (to get the backtrace and find the line of code)