Details

This message is generated when the value of the Jacobian option does not have the required form, or when the corresponding derivatives are not numerical at the indicated point.
This error can occur if a point is encountered at which the derivatives of the equations are singular or non-numerical, or if the value of the Jacobian option includes symbolic parameters that do not have numerical values.
Off[message] switches off the message; On[message] switches it on. For example: Off[General::njnum].

Examples

The first argument includes a symbolic parameter that does not have a numerical value:

This shows a valid value for the Jacobian option in FindRoot:

The derivative of the first argument is singular at the starting point:

This error can be avoided by choosing a different starting value:

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