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DiscreteDelta

DiscreteDelta
gives the discrete delta function , equal to if all the are zero, and otherwise.
Use in sums:
In[1]:=
Click for copyable input
Out[1]=
 
Use in sums:
In[1]:=
Click for copyable input
Out[1]=
One-argument form:
Multi-argument form:
Arguments can be approximate numbers:
TraditionalForm typesetting:
Use in sums to pick out terms:
Pick out elements:
Patch pointwise values of piecewise-defined functions:
Reduce an equation containing DiscreteDelta:
The support of DiscreteDelta has measure zero:
DiscreteDelta can stay unevaluated with numeric arguments:
A larger setting for $MaxExtraPrecision can be needed:
Equality testing of the arguments takes numerical precision into account:
New in 4