fdim
From cppreference.com
                    
                                        
                    
                    
                                                            
                    |   Defined in header  
<math.h>
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|   float       fdimf( float x, float y ); 
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(since C99) | |
|   double      fdim( double x, double y ); 
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(since C99) | |
|   long double fdiml( long double x, long double y ); 
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(since C99) | |
Returns the positive difference between x and y. This could be implemented as fmax (x - y, 0), so if x ≤ y, the result is always equals to 0, otherwise it is x - y.
[edit] Parameters
| x, y | - | floating point value | 
[edit] Return value
The positive difference value.
[edit] See also
|    (C99) 
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   computes absolute value of an integral value (|x|)  (function)  | 
|    (C99) 
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   larger of two floating point values   (function)  | 
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C++ documentation for fdim
 
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