add a little support for disabling dependencies in checkDependency.

this test will also serve to add a little coverage for simulateODE

systems/plants/test/simulinkDependency.m

@@ -1,10 +1,7 @@
 function simulinkDependency
 % tests that I can load the RBM without loading simulink
 
-if ~checkDependency('simulink')
-  disp('no worries.  you don''t even have simulink installed');
-  return;
-end
+checkDependency('simulink');  
 
 if verLessThan('matlab','8.3') % 2014a
   disp('I know it doesn''t work on 2012b, but haven''t tested 2013');
@@ -24,7 +21,16 @@
   error('oops.  simulink got loaded');
 end
 
-xtraj = simulate(r,[0 1]);
+checkDependency('simulink','disable');
+xtraj = simulate(r,[0 1]);  % this should run w/ simulateODE
+
+a = strfind(inmem,'Simulink');
+if ~isempty([a{:}])
+  error('oops.  simulink got loaded');
+end
+
+checkDependency('simulink','enable');
+xtraj = simulate(r,[0 1]);  % this should run w/ simulink
 
 a = strfind(inmem,'Simulink');
 if isempty([a{:}])

util/checkDependency.m

@@ -1,16 +1,29 @@
-function ok = checkDependency(dep,minimum_version)
+function ok = checkDependency(dep,command)
 % Drake code which depends on an external library or program should
 % check that dependency by calling this function.
 %   example:
 %     checkDependency('snopt')
 % or
 %     if (~checkDependency('snopt')) error('my error'); end
+%
+% @param dep the name of the dependency to check
+% @param command can be 'disable', 'enable'
+%  % todo: consider supporting a minimum_version
 
 persistent conf;
 
 ldep = lower(dep);
 conf_var = [ldep,'_enabled'];
 
+if (nargin>1)
+  if strcmp(command,'disable')
+    conf.(conf_var) = false;
+    return;
+  elseif strcmp(command,'enable')
+    conf.(conf_var) = [];
+  end
+end
+
 already_checked = isfield(conf,conf_var) && ~isempty(conf.(conf_var));
 if already_checked
   ok = conf.(conf_var);