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Think Julia by Allen B. Downey, Ben Lauwens

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Chapter 3. Functions

In the context of programming, a function is a named sequence of statements that performs a computation. When you define a function, you specify the name and the sequence of statements. Later, you can “call” the function by name.

Function Calls

We have already seen one example of a function call:

julia> println("Hello, World!")
Hello, World!

The name of the function is println. The expression in parentheses is called the argument of the function.

It is common to say that a function “takes” an argument and “returns” a result. The result is also called the return value.

Julia provides functions that convert values from one type to another. The parse function takes a string and converts it to any number type, if it can, or complains otherwise:

julia> parse(Int64, "32")
32
julia> parse(Float64, "3.14159")
3.14159
julia> parse(Int64, "Hello")
ERROR: ArgumentError: invalid base 10 digit 'H' in "Hello"

trunc can convert floating-point values to integers, but it doesn’t round off; it chops off the fraction part:

julia> trunc(Int64, 3.99999)
3
julia> trunc(Int64, -2.3)
-2

float converts integers to floating-point numbers:

julia> float(32)
32.0

Finally, string converts its argument to a string:

julia> string(32)
"32"
julia> string(3.14159)
"3.14159"

Math Functions

In Julia, most of the familiar mathematical functions are directly available. The following example uses log10 to compute a signal-to-noise ratio in decibels (assuming that signal_power and noise_power ...

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