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logarithmic axis can only plot positive values. There simply is no way to put negative values or zero on a logarithmic axis.
Fundamental: If 10L = Z, then L is the logarithm (base 10) of Z. If L is a negative value, then Z is a positive fraction of less than 1.0. If L is zero, then Z equals 1.0. If L is greater than 0, then Z is greater than 1.0. Note that there no value of L will result in a value of Z that is zero or negative. Logarithms are simply not defined for zero or negative numbers.