Derivative of vector-valued function

[abrock]

Derivative calculation works for scalar-valued functions:

In[56]:= p[x_] := x^2
In[57]:= p'[x]
Out[57]= 2 x

But not for vector-valued functions:

In[58]:= p[x_] := {x^2}
In[59]:= p'[x]
Out[59]= {0}

I was expecting {2x}.

[abrock]

Integration in contrast works just fine:

In[68]:= Integrate[{t, t^2}, {t,0,1}]
Out[68]= {1 / 2, 1 / 3}

[bnjones]

Another example:

In[7]:= D[{#^2}, #]
Out[7]= {0}

In[8]:= D[{x^2}, x]
Out[8]= {2 x}

I think this is related to this rule in mathics/builtin/calculus.py:

 'D[{items___}, x_?NotListQ]': 'D[#, x]& /@ {items}',

When this is applied to D[{#^2}, #], x gets bound to # and interpolated directly into a Function expression, which I think is where this goes wrong. We end up with D[#^2, #^2] which evaluates to zero (which isn't right either but that's not related to this issue).

There might be some other issues here but a short-term fix is to avoid slots in these rules, so we can properly handle taking derivatives of slot expressions.

[bnjones]

This should now be fixed. Thanks for reporting this!