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    i don't know what on earth i'm doing wrong here.

    i have

    restart;
    assume(hbar,positive);
    assume(omega,positive);
    assume(alpha,positive);
    assume(m,positive);
    f1:= (x,alpha)-> piecewise(abs(alpha*x)<=Pi/2,cos(alpha*x),0):
    f1(x,alpha);
    Df1:=diff(f1(x,alpha),x,x);

    now Df1 displays that  \cases{0& x&lt;-1/2\,{\frac {\pi }{{\it alpha}}} \cr {\it undefined}& x=-1/2\,{\frac {\pi }{{\it alpha~}}} \cr -\cos \left( {\it alpha~}\,x \right) {{\it alpha~}}^{2}& x&lt;1/2\,{\frac {\pi }{{\it alpha}}} \cr {\it undefined}& x=1/2\,{\frac {\pi }{{\it alpha}}} \cr 0& 1/2\,{\frac {\pi }{{\it alpha~}}}&lt;x \cr}
    don't know why that code above isn't working but basically Df1 says f1'' is undefined at pi/(2*alpha).

    as far as i'm aware the f_1''(x)=0 at x=-\frac{\pi}{2 \alpha},\frac{\pi}{2 \alpha} since \cos{\frac{\pi}{2}}=-\cos{\frac{\pi}{2}} and this is screwing up the rest of my worksheet. what am i doing wrong?

    i attach the LaTeX code for the bit i can't get working in case you want to try and get it working to see it properly:
    \cases{0& x<-1/2\,{\frac {\pi }{{\it alpha}}} \cr {\it undefined}& x=-1/2\,{\frac {\pi }{{\it alpha~}}} \cr -\cos \left( {\it alpha~}\,x \right) {{\it alpha~}}^{2}& x<1/2\,{\frac {\pi }{{\it alpha}}} \cr {\it undefined}& x=1/2\,{\frac {\pi }{{\it alpha}}} \cr 0& 1/2\,{\frac {\pi }{{\it alpha~}}}<x \cr}
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    never mind. realised where the problem was.
 
 
 
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Updated: January 27, 2010
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