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When I integrate the product of two DiracDelta functions, I get a single DiracDelta, i.e., Integrate[DiracDelta[x-y] DiracDelta[x-z],{x,-Infinity,Infinity}] = DiracDelta[y-z] as expected. However, sometimes the integral of a product of DiracDelta functions does not give the correct result. For instance one would expect: Integrate[DiracDelta[u+z(1-x)] DiracDelta[v-z y], {z,-Infinity,Infinity}] = DiracDelta[v(1-x)+u y] but instead gets a convergence error:Read more

Here is the simplified code: e[t_]:=DiracDelta[t] Exp[-I omegaC t] R[t1_] := Exp[-I omega21 t1] Integrate[R[t1]*e[t- t1], t1,Assumptions -> {t1 >= 0, t >= t1}] It doesn’t calculate, just return the input. I don’t know why, the integrated expression is simple.Read more