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Update Approx documentation

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Fixes #1328
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Martin Hořeňovský 2018-07-05 17:28:00 +02:00
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docs/assertions.md
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@ -55,33 +55,32 @@ This expression is too complex because of the `||` operator. If you want to chec
When comparing floating point numbers - especially if at least one of them has been computed - great care must be taken to allow for rounding errors and inexact representations. When comparing floating point numbers - especially if at least one of them has been computed - great care must be taken to allow for rounding errors and inexact representations.
Catch provides a way to perform tolerant comparisons of floating point values through use of a wrapper class called ```Approx```. ```Approx``` can be used on either side of a comparison expression. It overloads the comparisons operators to take a tolerance into account. Here's a simple example: Catch provides a way to perform tolerant comparisons of floating point values through use of a wrapper class called `Approx`. `Approx` can be used on either side of a comparison expression. It overloads the comparisons operators to take a tolerance into account. Here's a simple example:
``` ```cpp
REQUIRE( performComputation() == Approx( 2.1 ) ); REQUIRE( performComputation() == Approx( 2.1 ) );
``` ```
This way `Approx` is constructed with reasonable defaults, covering most simple cases of rounding errors. If these are insufficient, each `Approx` instance has 3 tuning knobs, that can be used to customize it for your computation. This way `Approx` is constructed with reasonable defaults, covering most simple cases of rounding errors. If these are insufficient, each `Approx` instance has 3 tuning knobs, that can be used to customize it for your computation.
* __epsilon__ - epsilon serves to set the percentage by which a result can be erroneous, before it is rejected. By default set to `std::numeric_limits<float>::epsilon()*100`. * __epsilon__ - epsilon serves to set the percentage by which a result can differ from `Approx`'s value before it is rejected. By default set to `std::numeric_limits<float>::epsilon()*100`.
* __margin__ - margin serves to set the the absolute value by which a result can be erroneous before it is rejected. By default set to `0.0`. * __margin__ - margin serves to set the the absolute value by which a result can differ from `Approx`'s value before it is rejected. By default set to `0.0`.
* __scale__ - scale serves to adjust the epsilon's multiplicator. By default set to `0.0`. * __scale__ - scale is used to change the magnitude of `Approx` for relative check. By default set to `0.0`.
#### epsilon example #### epsilon example
```cpp ```cpp
Approx target = Approx(100).epsilon(0.01); Approx target = Approx(100).epsilon(0.01);
100.0 == target; // Obviously true 100.0 == target; // Obviously true
200.0 == target; // Obviously still false 200.0 == target; // Obviously still false
100.5 == target; // True, because we set target to allow up to 1% error 100.5 == target; // True, because we set target to allow up to 1% difference
``` ```
#### margin example #### margin example
_Margin check is used only if the relative (epsilon and scale based) check fails._
```cpp ```cpp
Approx target = Approx(100).margin(5); Approx target = Approx(100).margin(5);
100.0 == target; // Obviously true 100.0 == target; // Obviously true
200.0 == target; // Obviously still false 200.0 == target; // Obviously still false
104.0 == target; // True, because we set target to allow absolute error up to 5 104.0 == target; // True, because we set target to allow absolute difference of at most 5
``` ```
#### scale #### scale