Manual Page for Command >>>> PERTURB


Syntax
>>>> PERTURB: (-)alpha (%)

Parent Command
all third-level commands in block > PARAMETER

Subcommand
-

Description
This command specifies the perturbation factor alpha for numerical computation of the Jacobian matrix. The columns of the Jacobian matrix are calculated by perturbing the corresponding parameter p by a small amount dp, and taking either a forward or centered finite difference quotient. The perturbation is usually a fraction of the parameter value itself:

dp = alpha * p

The default value for alpha is 1 %, which can be changed globally for all parameters using the third-level command >>> PERTURB, or individually for each parameter using the fourth-level command >>>> PERTURB. A negative value can be provided to specify a constant perturbation, independent of parameter value:

dp = |-alpha|

This option is sometimes required for parameters having either very small or very large values (such as initial pressure, generation times, or residual gas saturation).

Example
> PARAMETER
>> TIME at which production rate changes
>>> SOURCE: WEL_3
>>>> INDEX of array F1 : 5
>>>> initial GUESS : 1.7E8 seconds
>>>> PERTURB by constantly : -3.6E3 seconds
<<<<
<<<
<<
> COMPUTATION
>> JACOBIAN
>>> all other parameters are PERTURBed by : 2 % of their values
<<<
<<

See Also
>>> PERTURB


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Page updated: July 29, 1997