Why is evaluating this expression problematical?
y1(x)=x^2;y2(x)=5-x;
a0=1;an=3;Delta=(an-a0)/n;p(k)=a0+(k-1/2)*Delta;
I(n)=sum(abs(y2(p(k))-y1(p(k)))*Delta,k,1,n);
N(I(10))
SAGE respons:
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "_sage_input_109.py", line 9, in <module>
open("___code___.py","w").write("# -*- coding: utf-8 -*-\n" +
_support_.preparse_worksheet_cell(base64.b64decode("eTEoeCk9eF4yO3kyKHgpPTUteDsKYTA9MTthbj0zO0RlbHRhPShhbi1hMCkvbjtwKGspPWEwKyhrLTEvMikqRGVsdGE7Ckkobik9c3VtKGFicyh5MihwKGspKS15MShwKGspKSkqRGVsdGEsaywxLG4pOwpOKEkoMTApKQ=="),globals())
+"\n"); execfile(os.path.abspath("___code___.py"))
File "", line 1, in <module>
File "/tmp/tmpk0DnhJ/___code___.py", line 6, in <module>
N(I(_sage_const_10 ))
File "", line 1, in <module>
File "/home/sage/sage/local/lib/python2.6/site-packages/sage/misc/
functional.py", line 1165, in numerical_approx
return x.numerical_approx(prec)
File "expression.pyx", line 3797, in
sage.symbolic.expression.Expression.n (sage/symbolic/expression.cpp:
17022)
TypeError: cannot evaluate symbolic expression numerically
If I leave out the N( )-operator on the last line the block evaluates
to
1/500*sum(abs(-4*k^2 - 56*k + 329), k, 1, 10)
which can be evaluated in a new inputbox. Why not in one step?
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