tonight's lectures

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+Bistability in 2 variable systems
+
+review: mutual activation (positive feedback loop) 
+        and mutual inhibition (negative feedback loop)
+
+[review of simple mutual activitation and inhibition physical systems]
+
+when doing analysis, often want to plot nullclines in phase (aka, variable)
+space. the nullcline of a variable is a curve in phasespace where the time derivative of the given variable is zero.
+
+find these by expressing the differential of the variable (w/r/t time) as a
+symbolic expression (probably involving both variables) and solving for equals
+0. then we will analyse the intersecting points (which are equilibria, though
+not necessarily stable). might need to plot nullcline for varying "other"/free
+variables to find a state where there are 3x (or more) intersections, which are
+bistable systems.
+
+overall a bit confused; shouldn't this lecture have come earlier, before the
+stability analysis? oh, no, that was a single variable system.