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### What are you trying to do?


### What did you do?
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Please include a link to a minimal reproducer here. Preferably this
should be a complete runnable example at https://play.golang.org/.

If the issue involves a plot and can be replicated in an image.Image
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### What did you expect to happen?
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### What actually happened?
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### What version of Go and Gonum/plot are you using?
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### Does this issue reproduce with the current master?

