## Assorted Links (Economics)

*By dcerezo On 27/08/2012 · Leave a Comment · In economics, links*

- On Iterated Prisoner’s Dilemma contains strategies that dominate any evolutionary component: a hidden gem on one of the most celebrated results of the twentieth century.
- Why Central Planning?: some very interesting historical examples, but tyrants only caring about control? Really? Nah.
- US Monetary Policy since the Financial Crisis: the 2008 crisis was a liquidity crisis. And the Fed profited from the rescue.
- How Large is the Magnitude of Fixed-Mobile Substitution?
- Unveiling the Power Relationships within VC Firms

## To Err is CAS-possible

*By dcerezo On 26/08/2012 · Leave a Comment · In mathematics*

I was aware that there are too many errors on any CAS to be listed on the margin of their accompanying documentation. But finding the culprit after hours of debugging, a very simple bug but with a very high impact since other complex calculations are being based on its proper calculation, is a disturbing experience. It turns out that, in Mathematica,

**In[1]:= badIntegration ****= ****Integrate****[****1 ****/ (****2 ****+ ****Cos****[****x****])****, ****{****x, 0, y}, Assumptions ****-> ****y ****> Pi]**

**Out[1]:= 2(Pi+ ArcTan[Tan[y/2]/ Sqrt(3))/Sqrt(3)**

is symbolically evaluated as a discontinuous function, even if it must clearly be continuous, since the integrand is everywhere continuous, finite and positive. But the Weierstrass substitution method used internally when symbolically calculating integrals of inverse trigonometric functions sometimes produces discontinuities. Go figure.

Lesson learned: as a safety measure, always use multiple CAS programs (SAGE, Maple, …) to compare solutions when getting strange results.

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