# Multiple 'x' in policy equations not working

I am trying to mod an effect with the equation, 0.3*x^0.25-0.15*x. It does not work. Plotting software says it should look like this: What I get is this:

Not only too small, but decaying to 0.

If I remove the ‘0.3’ multiplier ‘eq=x^0.25-0.15*x’ it gives the correct shape:

If I rearrange it to ‘0-(0.5*x)+x^0.25’ I get this, which is laughably wrong:

I cannot figure out for the life of me what’s going on. Help.

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I assume these are what happened.

It seems using multiple Xs is okay but calculation of equations has an order.

[var0] {operator0} ( [var1] {operator1} [var2] ) {operator2} [var3] …

An equation will be processed in order of op1 - op2 - … - op0. So I guess these were your actual equations.

`0.3 * ( x ^ 0.25 - x ) * 0.15`

`x ^ ( ( 0.25 - x ) * 0.15 )`

`0 - ( 0.5 * x + x ) ^ 0.25`

Therefore, I think you will get what you want by using this equation instead.

`x*(x^-0.75)*0.3-0.15`

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Therefore, I think you will get what you want by using this equation instead.

``````x*(x^-0.75)*0.3-0.15
``````

Thank you! That worked. A weird way of writing it though!

…well, I thought it worked, but when the policy is set to 0 it shoots to infinity (or more accurately “-1.#J%”) rather than 0. So that’s a fun new problem.

Ohhhhh my bad. forgot that div by zero. the simplest take would be modifying it to `x*(x+0.001)^-0.75*0.3-0.15` but not sure how many operators are allowed so it will need further experimentation.