.. _method-nl2sol-x_conv_tol:

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x_conv_tol
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X-convergence tolerance


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**Specification**

- *Alias:* None

- *Arguments:* REAL

- *Default:* -1. (use NL2SOL internal default)


**Description**


``x_conv_tol`` maps to the internal NL2SOL control ``xctol``.
It is the X-convergence tolerance (scaled relative
accuracy of the solution variables).

The internal default is a function of machine epsilon
(as limited by ``function_precision``). The default is selected with a value of -1.