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0 pointsadrian_b2y ago0 comments

There is no need for that definition.

It is possible to completely remove the e^x function from mathematics without losing anything.

It is possible to express everything using a pair of functions, the real function 2^x and the complex function 1^x.

Then the cosinus and the sinus are the real and imaginary parts of 1^x (where x is measured in cycles a.k.a. turns).

The only disadvantage of this approach is that symbolic differentiation and integration are more complicated, by multiplication with a constant.

In my opinion the simplifications that are introduced everywhere else are more important than this disadvantage.

The real and complex function e^x was preferable in the 19th century, when numeric computations were avoided as too difficult and simple problems were solved by symbolic computation done with pen and paper.

Now, when anything difficult is done with a computer, both the function e^x and associated units like the radian and the neper are obsolete.

When programming computations on a computer, using 2^x and 1^x results in simpler and more accurate computations.

Moreover, when doing real physical measurements it is possible to obtain highly accurate values when the units are cycle and octave, but not when they are radian and neper.

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scythe2y ago

The function 1^x is constant everywhere. You can write (-1)^x to get the kind of effect you are looking for, but doing this with 1^x is madness.

>The only disadvantage of this approach is that symbolic differentiation and integration are more complicated, by multiplication with a constant.

There is more to it than that. The exponential function is not really e^x, it is lim_{N->∞} (1 + x/N)^N. The advantage of this definition is that, since it is valid everywhere on the complex plane, it allows the rigorous definition of real powers without recourse to inverse functions. We still teach students to prove things.

But also, isn't this a little contradictory? The goal of the original blog post was to simplify various differential equations. If you aren't simplifying symbolic differentiation, then what are you simplifying?

kandel2y ago

Mind explaining how to express some simple functions? Im interested

adrian_bOP2y ago

All mathematical formulas can be inter-converted based on the identity:

e^(x + i*y) = 2^(x/ln2) * 1^(y/2Pi)

Most formulae from textbooks are written in such a way to be simpler with e^x and its inverse, but it is almost always possible to move the constants ln2 and 2Pi between various equations so that in the end they will disappear from most relations, with the exception of the derivation or integration formulae.

In most applications, more equations are simplified than those which become more complicated.

A very important advantage of 2^x and 1^x versus e^x is that for the former the reductions of the argument to the principal range where the function is approximated by a polynomial can be done with perfect accuracy and very quickly, unlike for the latter. Moreover, for the former it is easy to verify the accuracy of any approximation, because for any argument that is represented as a binary number the functions 2^x and 1^x can be computed with a finite number of sqrt invocations (based on the formulae for half angle) and sqrt can be computed with any number of desired digits. Computing e^x with an arbitrary precision is trickier, because it requires criteria for truncation of an infinite series.

It should be noted that 1^1.0 = 1, 1^0.5 = -1, 1^0.25 = i, 1^0.75 = -i

kandel2y ago

so you express x (the simple polynomial) as ln(2^(x/ln2)? or as an infinite series expansion?

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