Question: Problem in plotting

I have the solution to a heat PDE, v and the error esitmate u + cos(x+t) = v


I want to plot log v(1,t) as function of log u(1,t) in maple, but I seem to get an error:

Error, (in plot) unexpected option: ln(u(1, t))


I am attaching my code below.

How to fix this problem?

Thanks in advance.

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