# BigDecimal Mode

With Jep 3, it is now possible to evaluate expressions using decimal arithmetic. This allows calculations to be performed with specified accuracy or even unlimited accuracy. If you are running into precision problems or already know that you will require the highest possible precision in your calculations, we recommend using this operation mode.

Rather than using the `double` type to represent numbers, `BigDecimal` is used. The `BigDecimal` class is part of the Java API and is contained in the `java.math` package. For more information on this class, please read the Sun Javadocs for BigDecimal.

The difference in the accuracy is best shown through an example. When performing multiplication of two numbers of the `double` type,

10*0.09 evaluates as 0.8999999999999999.

But when performing the same calculation using decimal arithmetic with the `BigDecimal` type,

10*0.09 evaluates as 0.9.

Note, care is needed when using BigDecimls as

10.0*0.09 evaluates as 0.90.

a subtly different BigDecimal value.

## How to use BigDecimal mode

Using Jep in BigDecimal mode is simple. Simply create a new Jep instance using the BigDecComponents with:

```import com.singularsys.jep.bigDecimals.BigDecComponents;

...

jep = new Jep(new BigDecComponents());```

This initializes Jep with a special the BigDecNumberFactory, BigDecOperatorTable and BigDecFunctionTable. By default, the math context is set to unlimited precision. But you can also initialize the components with a different math context. For example, to use 32-bit precision numbers simply use

`jep = new Jep(new BigDecComponents(MathContext.DECIMAL32));`

For more information about MathContexts refer to the Sun MathContext Javadocs.

## Supported Operators and Functions

Guaranteeing precision unfortunately comes at the cost of more complex algorithms for basic operators and functions. For this reason, some of the functions and operators available for `double` arithmetic are not available in the BigDecimal mode.

The supported operators and functions are below. These are all available by default with the BigDecComponents.

+, -, *, /, ^ (power), % (modulus)

>, <, >=, <=, == (equals)

&& (and), || (or), ! (not)

Functions Description Class
`round(val)`,
`round(val,dp)`
Round numbers. Two argument version round to a specific number of decimal places. BigDecRound
`rint(val)`
`rint(val,dp)`
Round numbers, with the round half even rounding mode. BigDecRound
`ceil(val)`
`floor(val)`
Floor and ceiling functions. BigDecRound
`roundSF(val,sf)` Round numbers to a specified number of significant figures. BigDecRoundSigFig
`abs(val)` Absolute value function. BigDecAbs
`signum(val)` Sign of the argument either -1, 0 or 1. BigDecSignum
`if(cond, true_val, false_val)` If function. If
`min(val1,val2,...)`
`max(val1,val2,...)`
Min and Max functions. BigDecTieBreakComparative,
MinMax
`avg(val1,val2,...)` Average Average

Just like with Jep in standard mode, you can add your own custom functions.

## BigDecimal and Strings

By default BigDecimal and Strings cannot be used together but as of release 3.4 this can now be turned on. The following code switches on this facility and adds the standard string functions.

```        // Create the BigDecComponents
BigDecComponents compSet = new BigDecComponents(MathContext.DECIMAL64,true);
// Create a jep instance
jep = new Jep(compSet);
// Add the standard set of string functions
jep.setComponent(new StringFunctionSet());
```

The above code will allow strings to be concatenated using '+' and compared using '==', '!=', '<', '<=', '>=', '>'. The StringFunctionSet allows the left, right, lower, upper, substring, len, mid, trim.