From: nma@12000.org   
      
   On 3/10/2021 12:35 PM, clicliclic@freenet.de wrote:   
   >   
   > "Nasser M. Abbasi" schrieb:   
   >>   
   >> On 3/4/2021 4:29 PM, Nasser M. Abbasi wrote:   
   >>>   
   >>> Only thing so far I found which I did not like too much, is   
   >>> when taking derivative of expression Z w.r.t say x, one   
   >>> has to define the derivative part w.r.t. x, on a separate line,   
   >>> then apply it on the expression on next line. Like this:   
   >>>   
   >>> ============   
   >>> @variables x y;   
   >>> D = Differential(x)   
   >>> ....few line later one can do....   
   >>> D(y) # Differentiate y wrt. x   
   >>> ==========   
   >>>   
   >>> One can't write on same line   
   >>>   
   >>>         diff(y(x),x)   
   >>>   
   >>> as normally with say Maple or Mathematica, etc... which   
   >>> for me is more clear since one sees the expression and the   
   >>> variable x, on same line. May be there is a way around   
   >>> this.   
   >>   
   >> Ok, figured it out   
   >> ==========================   
   >> julia> using Symbolics;   
   >> julia> @variables x y;   
   >> julia> y=x^2*sin(x);   
   >> julia> expand_derivatives(Differential(x)(y))   
   >>   
   >> cos(x)*(x^2) + 2x*sin(x)   
   >> ============================   
   >>   
   >> So   
   >>               diff(y,x)   
   >>   
   >> translates to   
   >>   
   >>               expand_derivatives(Differential(x)(y))   
   >>   
   >   
      
      
   > This forces one to type 38 instead of 9 characters. I suspect that the   
   > "expand_derivatives()" can be replaced by some general-purpose command   
   > like "evaluate()", however.   
   >   
   > Does the system distinguish upper from lower case? Would "differential"   
   > or "Expand_derivatives" thus fail?   
   >   
   > Martin.   
   >   
      
   It will fail yes, Julia is Case sensitive.   
   The reason for expand_derivatives is because Differential   
   is a "lazy" operator. So this causes it to evaluate.   
      
   I agree, it is much more verbose than  "diff(y,x)" or "D[y,x]"   
   but that is the only way I found to have the expression and   
   the differentiation variable show up on same line.   
      
   I am sure one can write a function to wrap all this in,   
   call it "diff(expression,variable)", to reduce the typing to do each time.   
      
   --Nasser   
      
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