Fix Derivative import from sympy

Author: kpeeters

core/DisplaySympy.cc

@@ -574,13 +574,30 @@ void DisplaySympy::import(Ex& ex)
 
 			// Move child nodes of partial to the right place.
 			if(*it->name=="\\partial") {
-				// std::cerr << Ex(it) << std::endl;
 				auto args = ex.begin(it);
 				++args;
 				while(args!=ex.end(it)) {
 					auto nxt=args;
 					++nxt;
-					ex.move_before(ex.begin(it), args)->fl.parent_rel=str_node::p_sub;
+					auto loc = ex.move_before(ex.begin(it), args);
+					loc->fl.parent_rel=str_node::p_sub;
+
+					// If the argument is \comma{x}{n} expand this to 'n' arguments 'x'.
+					// This is to handle Sympy returning 'Derivative(f(x), (x,2))' for the
+					// 2nd order derivative.
+
+					if(*loc->name=="\\comma") {
+						auto x=ex.begin(loc);
+						auto n=x; ++n;
+						if(! n->is_integer()) 
+							throw RuntimeException("DisplaySympy::import received un-parseable Derivative expression.");
+						int nn=to_long(*n->multiplier);
+						for(int k=0; k<nn; ++k)
+							ex.insert_subtree(loc, x);
+						ex.erase(loc);
+						}
+					
+					
 					args=nxt;
 					}
 //				ex.flatten(comma);

web2/cadabra2/source/download.html

@@ -11,8 +11,9 @@ <h1>Download and install</h1>
 <h2>Binary packages</h2>
 <p>
   Packages for various Linux distributions and for Windows (beta!) are
-  available for download here. They get updated on a semi-regular
-  basis by yours truly.
+  available for download here. Installation on macOS can be done
+  through HomeBrew; see below. All these packages get updated on a
+  semi-regular basis by yours truly; if you run into trouble, email me.
 </p>
 <p>
   Note that if your distribution has a <code>cadabra</code> package, this
@@ -101,15 +102,24 @@ <h2>Binary packages</h2>
 	 <div class="distronum"><a href="https://cadabra.science/packages/debian9">Debian Stretch 9</a></div>
   </div>
 
-<!--  <div class="distrotype">
+  <div class="distrotype">
 	 <img src="static/images/apple_logo.png"/>
 	 <div class="distronum">macOS</a></div>
 	 <div class="distrotxt">
-		Cadabra is available via the Homebrew package manager; just type
+		Cadabra is available via the Homebrew package manager. First
+		make sure that you have MacTeX installed, either by installing
+		it directly, or by using homebrew with
+		<code>brew tap caskroom/cask</code>
+		<code>brew cask install mactex</code>
+		After that, you can install Cadabra using
+		<code>brew tap kpeeters/repo</code>		
 		<code>brew install cadabra2</code>
-		to take care of installation.
+		Please not that this has not yet received a lot of testing; if
+		you encounter problems, please
+		email <a href="mailto:[email protected]">[email protected]</a>
+		so they can be fixed and other people can benefit from it.
 	 </div>
-  </div> -->
+  </div>
 
   <div class="distrotype">
 	 <img src="static/images/windows_logo.png"/>