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# Custom parameters
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The W-SLDA toolkit provides a framework for creating flexible parametrization of formulas. List of numbers (of double type) that can be passed from an input file to the code is called *custom parameters*. In the input file they start with tag:
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```bash
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# Custom parameters
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params0 0.0 # value of the parameter
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params1 1.0 # value of the parameter
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params2 2.0 # value of the parameter
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# ... and so on ...
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```
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Maximal number of parameters is specified in `predefines.h` by macro-variable:
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```c
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// Maximal number of parameters in params array
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#define MAX_USER_PARAMS 32
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```
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When the program reads the input file custom parameters are uploaded into `params` array in a such way that *paramsk* is assigned to `params[k]`. Pointer to the array is passed to each user-defined function, for example:
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```c
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double v_ext(int ix, int iy, int iz, int it, int spin, double *params, size_t extra_data_size, void *extra_data)
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{
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// ADD HERE FORMULA FOR V_ext(r)
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double V_ext = 0.0;
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return V_ext;
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}
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```
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During the self-iteration process, before `params` array is passed to user-defined functions the array can be processed by function:
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```c
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/**
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* THIS FUNCTION IS CALLED DURING THE SELF-CONSISTENT PROCESS.
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* After loading params array from input file, the parameters are processed by this routine.
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* The routine is executed at beginning of each iteration.
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* @param params array of size MAX_USER_PARAMS with parameters from input file.
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* @param kF typical Fermi momentum scale of the problem.
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* kF=referencekF if the referencekF tag is indicated in the input file,
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* otherwise to kF value is assigned according formula kF=(3*pi^2*n)^{1/3}, where n corresponds to maximal density.
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* You can also set kF at request in this function using (*kF)=myvalue;
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* @param mu array with chemical potentials: mu[SPINA] and mu[SPINB].
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* @param extra_data_size size of extra_data in bytes, if extra_data size=0 the optional data is not uploaded
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* @param extra_data optional set of data uploaded by load_extra_data()
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* */
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void process_params(double *params, double *kF, double *mu, size_t extra_data_size, void *extra_data)
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{
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// PROCESS INPUT FILE PARAMETERS
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}
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```
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Usage of `process_params( )` allows for parametrization of user-defined functions in terms of dimensionless values, which are typically more intuitive. For example:
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```bash
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params2 2.0 # barrier height, in units of chemical potential mu_a
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```
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and `process_params( )` converts *params2* into dimensional quantity
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```c
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void process_params(double *params, double *kF, double *mu, size_t extra_data_size, void *extra_data)
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{
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params[2]*=mu[SPINA]; // convert to dimensional form
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}
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```
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# Passing external data to user-defined functions
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To each user-defined function, arbitrary external data can be passed called *extra data*. The extra data is uploading before the self-consistent starts. In order to activate this option user must provide content of functions:
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```c
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/**
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* This function provides size of extra_data array, in bytes.
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* The extra_data of specified size will be allocated by the main process.
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* This function is thread-safe.
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* @param params with input file parameters.
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* NOTE: the array contains bare input file values, not processed by process_params()!
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* @return size of the extra_data array that needs to be allocated, if 0 then extra_data will not be allocated.
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* */
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size_t get_extra_data_size(double *params)
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{
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return 0;
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}
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```
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and
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```c
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/**
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* This function loads data into extra_data array.
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* This function is thread-safe.
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* @param size size of array computed using function get_extra_data_size()
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* @param extra_data pointer to array that should be filled with data
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* @param params with input file parameters.
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* NOTE: the array contains bare input file values, not processed by process_params()!
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* @return 0 if load is successful, otherwise return error code. If nonzero value is returned the main code will terminate.
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* */
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int load_extra_data(size_t size, void *extra_data, double *params)
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{
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return 0;
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}
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```
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# Predefined variables
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Each variable defined in `predefines.h` is accessible over entire file `problem-definition.h`. User can defined new variable in `predefines.h`, like
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```c
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#define MYVALUE 10.0;
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```
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which can be next used in user-defined functions:
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```c
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double v_ext(int ix, int iy, int iz, int it, int spin, double *params, size_t extra_data_size, void *extra_data)
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{
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// ADD HERE FORMULA FOR V_ext(r)
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double V_ext = MYVALUE; // it will assign value as given in predefines.h
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return V_ext;
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}
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``` |
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\ No newline at end of file |
