Using fractional exponent with bc

Question

bc, a Linux command-line calculator, is proficient enough to calculate

3^2
9

Even a negative exponent doesn't confuse it:

3^-2
0.11111

Yet it fails when it encounters

9^0.5
Runtime warning (func=(main), adr=8): non-zero scale in exponent

How could it be that bc can't handle this?

And what does the error message mean?

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Yes, I've read this and the solution given there:

e(0.5*l(9))
2.99999999999999999998

And yes, it is no good because of precision loss and

A calculator is supposed to solve expressions. You are not supposed to make life easier for the calculator, it is supposed to be the other way around...

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This feature was designed to encourage users to write their own functions. Making it a unique calculator that requires a user-defined function to calculate a square root.

It doesn't really bother me to write a function for tangents or cotangents as it looks pretty straightforward given s(x) and c(x). But in my opinion calculating a square root through a user-defined function is a bit too much.

Why anyone uses bc if there's Python out there? Speed?

Answer 1

In bc, b must be an integer in a ^ b. However you can add your own functions to bc like this:

create a file ~/.bcrc, add the following function to it:

define pow(a, b) {
    if (scale(b) == 0) {
        return a ^ b;
    }
    return e(b*l(a));
}

then you can start bc as follows:

bc ~/.bcrc -l

so you can use function pow to do such calculation.

See more here, you can add some more functions to bc.

Answer 2

bc is very basic and more complex functions not provided by the "math extension" must be implemented in the language itself: it has all you need to do it; in particular "power" is a common example even on wikipedia.

But you may be also interested in reading for example this answer here on SO.