Details

This message is generated when the second element in the data expression passed to LUBackSubstitution is not a list of integers in the required range.
This message can occur if a data expression is entered incorrectly.
A valid data expression can be obtained using LUDecomposition.
Off[message] switches off the message; On[message] switches it on. For example: Off[LUBackSubstitution::bpvt].

Examples

The second element in the data expression is not a list of positive integers:

Wolfram Language code: LUBackSubstitution[{{{1, 2}, {2, 1}}, {0, {}}, 1}, {1, 1}]

This shows a valid data expression in LUBackSubstitution:

Wolfram Language code: LUBackSubstitution[{{{1, 2}, {2, 1}}, {1, 2}, 1}, {1, 1}]

A valid data expression for use in LUBackSubstitution can be constructed using LUDecomposition:

Wolfram Language code: ludec = LUDecomposition[{{1, 2}, {2, 5}}]

Wolfram Language code: LUBackSubstitution[ludec, {1, 1}]

This particular example corresponds to solving a pair of linear equations:

Wolfram Language code: LinearSolve[{{1, 2}, {2, 5}}, {1, 1}]

Clear the value of ludec:

Wolfram Language code: Clear[ludec]

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