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Substitute piecewise function variable

asked 2017-03-24 14:39:26 -0600

jrojasqu gravatar image

I have the following piecewise function:

phi   = piecewise([([-1,1], (1-abs(x))*(1-abs(x))*(1+2*abs(x)))]);
phi   = phi.extension(0);

It appears to be a valid function since I can obtain/plot its values for any 'x'. But whenever I try to substitute the variable, it does not work. For example,

phi(2)
0

but if I declare another variable 'h' and try to input that variable into the piecewise function, it does not appear to work:

h=pi/2
phi(h)
TypeError: self must be a numeric expression

At first I thought that 'h' was not a 'numeric' or 'real' value, but when I test it, it is a real value:

h.is_real()
True

How can I overcome this? How can I successfully operate a variable substitution in my piecewise function?

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answered 2017-03-24 17:41:35 -0600

If you check the type of h with type(h), it comes back as

<type 'sage.symbolic.expression.Expression'>

which is not numeric but symbolic. You can convert it to a numeric value with n(h) or h.n() and then the substitution will give zero as expected.

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@paulmasson Thanks, it worked; and I would at least vote your answer but I lack the minimum 10 points to do so...

jrojasqu gravatar imagejrojasqu ( 2017-03-27 18:08:35 -0600 )edit

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Asked: 2017-03-24 14:39:26 -0600

Seen: 66 times

Last updated: Mar 24