In[]:=
initialExpr[u0_,x_,t_,k_]:=u0*(1-(1/Pi)*Integrate[Exp[-v*t]/v*Sin[Sqrt[v/k]*x],{v,0,Infinity},Assumptions->{t>0,k>0}])​​
In[]:=
eulerSubstitute=Sin[Sqrt[v/k]*x]->(Exp[I*Sqrt[v/k]*x]-Exp[-I*Sqrt[v/k]*x])/(2*I);​​​​
In[]:=
modifiedExpr=initialExpr[u0,x,t,k]/.eulerSubstitute
Out[]=
u01-Erf
x
2
kt
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