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→‎5.4 Complex Powers

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 === 5.4 Complex Powers ===
+Returning to the ambiguity problem of multi-valuedness, it seems the best way to avoid issues is when a particular choice of $$logw$$ has been specified.  As an example, $$w^z$$ with $$z=1/2$$.  We can specify a rotation for $$logw$$ to achieve $$+w^1/2$$, then another rotation of $$logw$$ to achieve $$-w^1/2$$.  The sign change is achieved because of the Euler formula <math>e^{π*i}=-1. Note the process:
+<math>w^z=e^{zlogw}=e^{zre^{iθ}}=e^{ze^iθ}}, then specifying rotations for theta allows us to achieve either $$+w^1/2$$ or $$-w^1/2$$.
+Penrose notes an interesting curiosity for the quantity $$i^i$$.  We can specify <math>logi=(1/2)πi</math> because of the general relationship <math>logw=logr+iθ</math>.  If $$w=i$$, then its easy to see <math>logi=(1/2)πi</math> from noting that y is on the vertical axis in the complex plane (rotation of $$π/2$$).  This specification, and all rotations, amazingly achieve real number values for i^i.
+We end the section with the idea of finite multiplicative groups, or cyclic groups $$\BbbZn$$, which contain $$n$$ quantities with the property that any two can be multiplied together to get another member of the group.  As an example, Penrose gives us w^z= e^ze^i(theta+2*pi*i*n) with n=3, leading to three elements 1, XX, XX^2 with XX=e^2*pi*i/3. Note XX^3=1 and XX^-1=XX^2.  These form a cyclic group Z3 and in the complex plane, represent vertices of an equilateral triangle.  Multiplication by XX rotates the triangle through 2/3*pi anticlockwise and multiplication by XX^2 turns it through 2/3*pi clockwise.
 == Chapter 6 Real-number calculus ==