error: cannot convert ‘array_type {aka boost::multi_array}’ to ‘double (*)[2]’

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I am a beginner in c++ and using boost library for the first time.
I have this program for solving a differential equation:

C#

double rk2(double(*)[2], double, double, double, double(*)[2], double);
int main()
{// Create a 2D array that is n X 2
  typedef boost::multi_array<double, 2> array_type;
  typedef array_type::index index;
  array_type a(boost::extents[n][2]);

 // Create a 2D array that is n X 2
  typedef boost::multi_array<double, 2> array_type;
 typedef array_type::index index;
  array_type v(boost::extents[n][2]);

Then I have some conditions followed by..

C#

 while 
{ (....some condition...)
       tf = ti + dt;
       vf = rk2(a,ti,vi,tf, v, xi);
       xi = vf*dt+xi;
}
 return 0;
}

then i define my function

C#

double rk2(double a[10000][2], double ti, double vi, double tf, double v[10000][2], double xi)
{ ....lines..
return vf;
}

I'm getting an error message saying:

HTML

error: cannot convert ‘array_type {aka boost::multi_array<double,>}’ to ‘double (*)[2]’ for argument ‘1’ to ‘double rk2(double (*)[2], double, double, double, double (*)[2], double)’

Please help me!

Posted 28-May-13 2:18am

Member 10072007

Updated 28-May-13 12:09pm

Kenneth Haugland

v3

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Comments

KarstenK 28-May-13 8:49am

using a fixed size for function parameters is always a bad idea.

Prefer using owned defined data types or second best arrays with variable dimension.

Rule of thumb: using defined data types helps a to avoid a mob of bugs. ;-)

[no name] 29-May-13 5:35am

I'm getting another error then, error: invalid types ‘double[int]’ for array subscript this error is coming while giving value of array to another variable: int l; eita = a[l][0]; what to do?

2 solutions

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JackDingler · Answer 1 · 2013-05-28T09:29:00

Solution 1

KarstenK is right.

To be clearer try this...

C++

double rk2(array_type & a, double ti, double vi, double tf, double v[10000][2], double xi)
{ ....lines..
return vf;
}

Posted 28-May-13 9:29am

JackDingler

Comments

[no name] 29-May-13 2:36am

I'm getting another error then,
error: invalid types ‘double[int]’ for array subscript
this error is coming while giving value of array to another variable:
int l;
eita = a[l][0];
what to do?

KarstenK 29-May-13 7:22am

You need to use matchtng types. For that reason you should carefully define the interface. Use the approbiate type.

Member 10072007 · Answer 2 · 2013-05-29T06:12:00

C#

using namespace std;
// Create a 2D array that is n X 2
typedef boost::multi_array<double, 2>two_d_array_type;
typedef two_d_array_type::index index;
// there is no need to name multi_array<double, 2> and index two times. We can do it here once and for all. Note that we defined it globally (outside any) function so that the new names that we have put are recognized by all functions
// I have put rk2 above main so that there is no need of an additional initial declaration
double rk2(two_d_array_type & a, double ti, double vi, double tf, two_d_array_type & v, double xi)
{...(lines)
return vf;
}

int main()
{ while 
{ (....some condition...)
       tf = ti + dt;
       vf = rk2(a,ti,vi,tf, v, xi);
       xi = vf*dt+xi;
}
 return 0;

}