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I'm a bit rusty in mathematics so I need your help please :)

I need a function $y$ that satisfies: $$\begin{align*} y &= ax\\ y &= \left\{\begin{array}{ll} x &\text{if }x\geq 0;\\ 0 &\text{if }x\lt 0. \end{array}\right. \end{align*}$$

Is there a way to do this? What should $a$ be like? I believe I need something that is $1$ for positive value and $0$ for negative.

Thank you

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    $y=x$ for $x\ge 0$ and $y=0$ for $x<0$ is already a complete definition of a function. This function fulfills $y=ax$ with $a=1$ for $x\ge0$ and with $a=0$ for $x<0$, so if you wanted the function to fulfill $y=ax$ everywhere with a single $a$, then that contradicts the other two conditions.2011-04-12
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    Guessing on the basis of Ross' answer: Did you mean you want $y=ax$ with different $a$ for positive and negative $x$? And does "something" in the last sentence refer to $a$? In that case, you've already got it all figured out correctly -- if you plug $a=1$ for $x\ge0$ and $a=0$ for $x<0$ into $y=ax$, you get $y=x$ for $x\ge0$ and $y=0$ for $x<0$.2011-04-12
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    Please spend some effort making your titles informative. "Anybody know a way to" is **not** informative.2011-04-12

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