Plotting a piecewise function

I'm having trouble plotting the piecewise function below. The only way I can replicate this function is using

Plot[Piecewise[{{x^2, x >= 0}, {0, x < 0}}], {x, -10, 10}]

When I define the piecewise function as:

unitstep[x] = Piecewise[{{x^2, x >= 0}, {0, x < 0}}]

and then plot unitstep[x], the graph turns out linear.

Am I missing something here?

Answer

You have apparently missed reading the documentation on defining functions.

If you define unitstep (not a good name) as follows

unitstep[x_] := Piecewise[{{x^2, x >= 0}, {0, x < 0}}]

then it plots as you would expect

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