Re: Mantaining the same form
- To: mathgroup at smc.vnet.net
- Subject: [mg124107] Re: Mantaining the same form
- From: Chris Young <cy56 at comcast.net>
- Date: Mon, 9 Jan 2012 03:17:51 -0500 (EST)
- Delivered-to: l-mathgroup@mail-archive0.wolfram.com
- References: <je9624$iqs$1@smc.vnet.net>
On 2012-01-07 10:16:36 +0000, Miguel Gil said: > At a function in which one parameter is an expression "expr", > Mathematica 8.0 evaluates or simplifies the value of "expr" when it is > introduced. > How is that Mathematica keep the same form of the "expr" introduced?. > > Example: > > In []: MyFunction [expr_]: = expr; > MyFunction [(Sin [2x], Tan [y]) / (x * Sec [y]^2)] > > Out []: (Cos [y]^2 (Sin [2x], Tan [y]) / x > > I want to get the same expression (Sin [2x], Tan [y]) / (x * Sec [y]^2) > > Clearly, the input expression and modified expression are equivalent, > but are not equal. > For example, if we were to apply the rule of L'Hopital or the theorem > Schwarz the results would be erroneous. I tried everything I could think of, but couldn't write any function that would just pass on the expression unchanged: In[264]:= exprHeld[e_] := Hold[e] In[265]:= exprHeld[(Sin[2 x] * Tan[y])/(x * Sec[y]^2)] Out[265]= Hold[(Cos[y] Sin[2 x] Sin[y])/x] In[266]:= holdAll[e_] := HoldAll[e] holdAll[(Sin[2 x] * Tan[y])/(x * Sec[y]^2)] Out[267]= HoldAll[(Cos[y] Sin[2 x] Sin[y])/x] In[268]:= holdComplete[e_] := HoldComplete[e] In[269]:= holdComplete[(Sin[2 x] * Tan[y])/(x * Sec[y]^2)] Out[269]= HoldComplete[(Cos[y] Sin[2 x] Sin[y])/x] In[270]:= uneval[e_] := Unevaluated[e]; In[271]:= uneval[(Sin[2 x] * Tan[y])/(x * Sec[y]^2)] Out[271]= (Cos[y] Sin[2 x] Sin[y])/x In[272]:= Hold[Unevaluated[(Sin[2 x] * Tan[y])/(x * Sec[y]^2)]] Out[272]= Hold[Unevaluated[(Sin[2 x] Tan[y])/(x Sec[y]^2)]] In[273]:= holdUneval[e_] := Hold[Unevaluated[e]] In[274]:= holdUneval[(Sin[2 x] * Tan[y])/(x * Sec[y]^2)] Out[274]= Hold[Unevaluated[(Cos[y] Sin[2 x] Sin[y])/x]] In[278]:= ToString[HoldComplete @ ((Sin[2 x] * Tan[y])/(x * Sec[y]^2)), InputForm] Out[278]= "HoldComplete[(Sin[2*x]*Tan[y])/(x*Sec[y]^2)]" In[279]:= heldString[e_] := ToExpression[ ToString[HoldComplete @ e, InputForm], InputForm]; In[280]:= heldString[(Sin[2 x] * Tan[y])/(x * Sec[y]^2)] Out[280]= HoldComplete[(Cos[y] Sin[2 x] Sin[y])/x]