User-defined-parameters.md

 # Custom parameters
 
-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:  
+The W-SLDA toolkit provides a framework for creating flexible parametrization of formulas. The 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 the tag:  
 ```bash
 # Custom parameters
 params0            0.0 # value of the parameter 
 params1            1.0 # value of the parameter
 params2            2.0 # value of the parameter
 # ... and so on ...
+# ... if you need pass string parameter...
+strings0           aaa
+strings1           bbb
 ```
 Maximal number of parameters is specified in `predefines.h` by macro-variable:  
 ```c
@@ -33,7 +36,7 @@ During the self-iteration process, before `params` array is passed to user-defin
  * @param params array of size MAX_USER_PARAMS with parameters from input file. 
  * @param kF typical Fermi momentum scale of the problem. 
  *           kF=referencekF if the referencekF tag is indicated in the input file, 
- *           otherwise to kF value is assigned according formula kF=(3*pi^2*n)^{1/3}, where n corresponds to maximal density.
+ *           otherwise to kF value is assigned according to formula kF=(3*pi^2*n)^{1/3}, where n corresponds to maximal density.
  *           You can also set kF at request in this function using (*kF)=myvalue;
  * @param mu array with chemical potentials: mu[SPINA] and mu[SPINB]. 
  * @param extra_data_size size of extra_data in bytes, if extra_data size=0 the optional data is not uploaded
@@ -86,6 +89,9 @@ and
  * */
 int load_extra_data(size_t size, void *extra_data, double *params)
 {
+    // ... for example 
+    // FILE *f=fopen(input->strings[0], "r");
+    // ...
     return 0;
 }
 ```