Manual Page for Command >>> PERTURB

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

Parent Command
>> JACOBIAN

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, independent of parameter value:

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:

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
> COMPUTATION
>> JACOBIAN
>>> PERTURBation factor alpha : 0.005 of parameter value
<<<
<<

See Also
>>> FORWARD | >>> CENTERED | >>>> PERTURB

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Page updated: July 29, 1997