# Plot and Parametric plot give different results [duplicate]

This question already has an answer here:

f[k_] = {{-0.001 - 2 I k, 1, -0.001, -0.501}, {0.001, -0.5 - I k, 0.001, 0.001},
{-0.001, -0.501, -0.001 + 2 I k, 1.}, {0.001, 0.001, 0.001, -0.5 + I k}};

x[k_] = Re[Eigenvalues[f[k]][[3]]];
Plot[x[k], {k, -1, 1}]
ParametricPlot[{k, x[k]}, {k, -1, 1}]


Why does Plot give a result, but ParametricPlot does not? Both functions are supposed to give the graph of the function x[k]. I don't understand why ParametricPlot returns nothing. Please help me to get the difference.

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## marked as duplicate by Sjoerd C. de Vries, bobthechemist, Michael E2, R. M.♦Jan 29 '14 at 20:18

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

It's because the aspectratio is bad in parametricplot – Coolwater Jan 28 '14 at 20:32
– Sjoerd C. de Vries Jan 28 '14 at 20:47
@Sjoerd It seems to me this may be considered a duplicate. Any reason you did not vote to close it as such? – Mr.Wizard Jan 29 '14 at 0:04
@Mr.Wizard I wasn't near my PC, so I couldn't check what "Why does Plot give a result, but ParametricPlot does not?" entailed. I assumed it would be like the linked question, but wasn't sure. Will vote to close now. – Sjoerd C. de Vries Jan 29 '14 at 17:56

## 1 Answer

Plot[x[k], {k, -1, 1}]


For the ParametricPlot you need to alter the Options to reproduce the plot.

ParametricPlot[{k, x[k]}, {k, -1, 1}, AspectRatio -> 1/2]


You can find out the default AspectRatio for Plot by doing:

Options[Plot, AspectRatio]


{AspectRatio -> 1/GoldenRatio}

OR more elegantly as suggested by Belisarius

p = Plot[x[k], {k, -1, 1}];
ParametricPlot[{k, x[k]}, {k, -1, 1}, Evaluate[AbsoluteOptions[p]]]

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p = Plot[x[k], {k, -1, 1}]; ParametricPlot[{k, x[k]}, {k, -1, 1}, Evaluate[AbsoluteOptions[p]]] – Dr. belisarius Jan 28 '14 at 20:35
@Belisarius. Nice – RunnyKine Jan 28 '14 at 20:37