Различные методы, в том числе заданные значения (которые необходимо установить после удержания).
Clear[σ23]
StressMatrix = Map[Hold,
{{σ11, σ12, σ13}, {σ21, σ22, σ23}, {σ31, σ32, σ33}}, {2}];
varList = {{ρ, θ, z}};
σ23 = 4 ρ^2;
expr = StandardForm[
"∂" <> StringTake[ToString[StressMatrix[[2, 3]]], {6, -2}]/
"∂" <> ToString[varList[[1, 1]]]];
symbolic = Inactive[D][ReleaseHold@StressMatrix[[2, 3]], varList[[1, 1]]];
result = D[ReleaseHold@StressMatrix[[2, 3]], varList[[1, 1]]];
Row[{expr, " = ", symbolic, " = ", result}]
Альтернативно
symbolic2 = StringJoin["D[",
StringTake[ToString[StressMatrix[[2, 3]]], {6, -2}], ",",
ToString@varList[[1, 1]], "]"];
Row[{expr, " = ", symbolic2, " = ", ToExpression[symbolic2]}]
И наконец
Clear[σ23]
StressMatrix =
Map[HoldForm, {{σ11, σ12, σ13}, {σ21, σ22, σ23}, {σ31, σ32, σ33}}, {2}];
varList = {{ρ, θ, z}};
σ23 = 4 ρ^2;
expr = StandardForm[
"∂" <> ToString[StressMatrix[[2, 3]]]/
"∂" <> ToString[varList[[1, 1]]]];
symbolic = Inactive[D][ToString@StressMatrix[[2, 3]], varList[[1, 1]]];
result = D[ReleaseHold@StressMatrix[[2, 3]], varList[[1, 1]]];
Row[{expr, " = ", symbolic, " = ", result}]
person
Chris Degnen
schedule
02.06.2017