The QROMO function evaluates the integral of a function over the open interval (*A, B*) using a modified Rombergâ€™s method.

## Examples

Consider the following function:

`FUNCTION hyper, X`

RETURN, 1.0 / X^4

`END`

This example integrates the HYPER function over the open interval (2, âˆž) and prints the result:

PRINT, QROMO('hyper', 2.0, /MIDEXP)

IDL prints:

` 0.0412050`

**Note: **When using the MIDEXP keyword, the upper integration limit is assumed to be infinity and is not supplied.

## Syntax

*Result* = QROMO(*Func*, *A* [, *B*] [, /DOUBLE] [, EPS=*value*] [, JMAX=*value*] [, K=*value*] [, /MIDEXP | , /MIDINF | , /MIDPNT | , /MIDSQL | , /MIDSQU] )

## Return Value

Returns the integral of the function.

## Arguments

### Func

A scalar string specifying the name of a user-supplied IDL function to be integrated. This function must accept a single scalar argument *X* and return a scalar result. It must be defined over the open interval (*A, B*).

For example, if we wish to integrate the fourth-order polynomial

y = 1 / x^{4}

we define a function HYPER to express this relationship in the IDL language:

`FUNCTION hyper, X`

RETURN, 1.0 / X^4

`END`

**Note: **If QROMO is complex then only the real part is used for the computation.

### A

The lower limit of the integration. *A* can be either a scalar or an array.

### B

The upper limit of the integration. *B* can be either a scalar or an array. If the MIDEXP keyword is specified, *B* is assumed to be infinite, and should not be supplied by the user.

Note: If arrays are specified for *A* and *B*, then QROMO integrates the user-supplied function over the interval [*A*_{i}, *B*_{i}] for each *i*. If either *A* or *B* is a scalar and the other an array, the scalar is paired with each array element in turn.

## Keywords

### DOUBLE

Set this keyword to force the computation to be done in double-precision arithmetic.

### EPS

The fractional accuracy desired, as determined by the extrapolation error estimate. For single-precision calculations, the default value is 1.0 x 10^{-6}. For double-precision calculations, the default value is 1.0 x 10^{-12}.

### JMAX

Set to specify the maximum allowed number of mid quadrature points to be 3^{(JMAX - 1)}. The default value is 14.

### K

Integration is performed by Rombergâ€™s method of order 2K. If not specified, the default is K=5.

### MIDEXP

Use the midexp() function (see *Numerical Recipes*, section 4.4) as the integrating function. If the MIDEXP keyword is specified, argument B is assumed to be infinite, and should not be supplied by the user.

### MIDINF

Use the midinf() function (see *Numerical Recipes*, section 4.4) as the integrating function.

### MIDPNT

Use the midpnt() function (see *Numerical Recipes*, section 4.4) as the integrating function. This is the default if no other integrating function keyword is specified.

### MIDSQL

Use the midsql() function (see *Numerical Recipes*, section 4.4) as the integrating function.

### MIDSQU

Use the midsqu() function (see *Numerical Recipes*, section 4.4) as the integrating function.

## Version History

4.0 |
Introduced |

## Resources and References

QROMO is based on the routine qromo described in section 4.4 of *Numerical Recipes in C: The Art of Scientific Computing* (Second Edition), published by Cambridge University Press, and is used by permission.