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POCalling GSL function inside a class in a shared library
 

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  1. POCalling GSL function inside a class in a shared library
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    <p>I'm trying make a shared library in c++ implementing tools for Fermi gases. I'm using the GSL library to solve a function numerically and my code runs without a problem without when running as a script, but when trying to convert it to a shared library and classes I encounter problems.</p> <p>I've seen similar questions: <a href="https://stackoverflow.com/questions/3194119/function-pointers-working-as-closures-in-c">Q1</a> <a href="https://stackoverflow.com/questions/13289311/c-function-pointers-with-c11-lambdas">Q2</a> <a href="https://stackoverflow.com/questions/13074756/how-to-avoid-static-member-function-when-using-gsl-with-c/18181494#18181494">Q3</a></p> <p>I'm fairly new to c++-programming and cannot seem to adapt the different answers to my problem. Probably since I do not quite understand the answers.</p> <p>My code is:</p> <pre><code>/* Define structure for the GSL-function: chempot_integrand */ struct chempot_integrand_params { double mu; double T; }; double ChemicalPotential::chempot_integrand (double x, void * params){ /* Computes the integrand for the integral used to obtain the chemical potential. * * This is a GSL-function, which are integrated using gsl_integration_qag. */ // Get input parameters. struct chempot_integrand_params * p = (struct chempot_integrand_params *) params; double mu = p-&gt;mu; double T = p-&gt;T; // Initiate output parameters for GSL-function. gsl_sf_result_e10 result; int status = gsl_sf_exp_e10_e( ( gsl_pow_2(x) - mu ) / T , &amp;result ); if (status != GSL_SUCCESS){ printf ("Fault in calculating exponential function."); } // Return (double) integrand. return (gsl_pow_2(x) / ( 1 + result.val * gsl_sf_pow_int(10,result.e10) )); } /* Define structure for the GSL-function: chempot_integration */ struct chempot_integral_params { double T; }; double ChemicalPotential::chempot_integration (double mu, double T){ /* Computes the integral used to obtain the chemical potential using the integrand: chempot_integrand. */ // Set input parameters for the integrand: chempot_integrand. struct chempot_integrand_params params_integrand = { mu, T }; // Initiate the numerical integration. gsl_integration_workspace * w = gsl_integration_workspace_alloc (1000); // Allocate memory for the numerical integration. Can be made larger if neccessary, REMEMBER to change it in the function call: gsl_integration_qag as well. double result, error; gsl_function F; F.function = &amp;ChemicalPotential::chempot_integrand; F.params = &amp;params_integrand; // Upper limit for integration double TOL = 1e-9; double upp_lim = - T * gsl_sf_log(TOL) + 10; gsl_integration_qag (&amp;F, 0, upp_lim, 1e-12, 1e-12, 1000, 6, w, &amp;result, &amp;error); // Free memory used for the integration. gsl_integration_workspace_free (w); return result; } </code></pre> <p>and when compiling I get the error</p> <pre><code>error: cannot convert ‘double (Fermi_Gas::ChemicalPotential::*)(double, void*)’ to ‘double (*)(double, void*)’ </code></pre> <p>in line</p> <pre><code>F.function = &amp;ChemicalPotential::chempot_integrand; </code></pre>
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    1. USRasmus Søgaard Christensen
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    1. COI suspect your ChemicalPotential::chempot_integrand method must be a static one, if you want to use it as a callback function to GSL.
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