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POGSL integration of a class member function
 

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  1. POGSL integration of a class member function
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    <p>I have a class called Universe. The class includes a member function to calculate distance and requires numerically integrating an ugly looking function. I was trying to use GSL to perform the integration but I get the following error when I attempt to compile the library - </p> <pre><code>$ g++ -c -O3 -std=c++11 Universe.cpp -o Universe.o $ error: cannot convert ‘Universe::Hz’ from type ‘double (Universe::)(double, void*)’ to type ‘double (*)(double, void*)’ </code></pre> <p>Here's the class Universe without the constructors (for brevity):</p> <h2>Universe.h</h2> <pre><code>#ifndef UNIVERSE_H #define UNIVERSE_H #include &lt;cmath&gt; #include &lt;gsl/gsl_integration.h&gt; using namespace std; class Universe { private: static constexpr double c = 299792458.0, Mpc2Km = 3.08567758e+19, Yrs2Sec = 3.15569e7; double H0 = 67.77, OmegaM = (0.022161+0.11889)/(H0*H0), OmegaL = 0.6914, OmegaG = 8.24e-5, OmegaK = 0.0009; double Ez(double z); double Hz(double z, void* params); public: double distH, timeH; Universe() = default; Universe(double h0); Universe(double omegaM, double omegaL); Universe(double h0, double omegaM, double omegaL); Universe(double omegaM, double omegaL, double omegaG, double omegaK); Universe(double h0, double omegaM, double omegaL, double omegaG, double omegaK); //double radius(); //double age(); double distC(double z); }; #endif </code></pre> <h2>Universe.cpp</h2> <pre><code>#include &lt;cmath&gt; #include &lt;gsl/gsl_integration.h&gt; #include "Universe.h" using namespace std; double Universe::Hz(double z, void* params) { double result = 1.0/pow(OmegaL + pow(1.0+z,3.0)*OmegaM + pow(1.0+z,4.0)*OmegaG + pow(1.0+z,2.0)*OmegaK, 0.5); return result; } double Universe::distC(double z) { double lower_limit = 0.0, abs_error = 1.0e-8, rel_error = 1.0e-8, alpha = 0.0, result, error; gsl_integration_workspace *work_ptr = gsl_integration_workspace_alloc(1000); gsl_function Hz_function; void* params_ptr = &amp;alpha; Hz_function.function = Universe::Hz; Hz_function.params = params_ptr; gsl_integration_qags(&amp;Hz_function, lower_limit, z, abs_error, rel_error, 1000, work_ptr, &amp;result, &amp;error); return distH*result; } </code></pre> <p>I don't quite know how to troubleshoot this problem and I'm using GSL for the first time based on the documentation at: <a href="http://www.gnu.org/software/gsl/manual/html_node/Numerical-integration-examples.html" rel="nofollow">http://www.gnu.org/software/gsl/manual/html_node/Numerical-integration-examples.html</a> and the following guide: <a href="http://www.physics.ohio-state.edu/~ntg/780/gsl_examples/qags_test.cpp" rel="nofollow">http://www.physics.ohio-state.edu/~ntg/780/gsl_examples/qags_test.cpp</a> Thank you for looking and any answers! </p>
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    1. COThere is a well known solution to your problem at [1] [1]: http://stackoverflow.com/questions/13074756/how-to-avoid-static-member-function-when-using-gsl-with-c/18181494#18181494
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