# Evaluate a single variable polynomial equation

# Challenge

Given a list of n numbers and x, compute $a + bx^1 + cx^{2} + ... + zx^{n-1}$, where a is the first value in the list, b is the second, etc. n is at most 256 and at least 0. The input value(s) can be any 32-bit float

Input can be in any format of choice, as long as it is a list of numbers and x. (And this'll likely stay this way, even if input rules change over time)

# Test inputs

`1.0`

, `182`

-> `1`

`1.0, 2.0`

, `4`

-> `9`

`2.5, 2.0`

, `0.5`

-> `3.5`

`1.0, 2.0, 3.0, 4.0`

, `1.5`

-> `24.25`

# Example ungolfed program (Rust)

```
// dbg! is a logging function, prints the expression and it's output.
// Good for seeing what's happening
// Test setup
pub fn main() {
let inp: &[f32] = &[1.0, 2.0, 3.0, 4.0];
let x: f32 = 1.5;
dbg!(evaluate_polynomial(inp, x)); // take inputs, print result
}
// Actual challenge answer function
pub fn evaluate_polynomial(inp: &[f32], x: f32) -> f32 {
let mut accum: f32 = 0.0;
for (idx, val) in inp.iter().enumerate() {
// x.pow(idx) * val
accum += dbg!(x.powf(idx as f32) * val);
}
return accum;
}
```

[APL (Dyalog Unicode)], 11 3 1 …

5mo ago

Japt `-x`, 6 5 bytes ËV …

5mo ago

Japt, 12 bytes ÊÆgX VpX …

5mo ago

[Raku], 19 bytes (Z …

5mo ago

[JavaScript (Node.js)], 40 byt …

5mo ago

Ruby, 50 bytes ```ruby def …

5mo ago

Vyxal, 6, 5, 4 bytes ``` Źe …

3mo ago

[Haskell], 20 bytes …

5mo ago

[Jelly], 1 byte ḅ Tr …

4mo ago

Ruby, 38 bytes Simple map and …

4mo ago

Pyth, 10 bytes sR^HhZhA …

3mo ago

## 11 answers

#
APL (Dyalog Unicode), ^{11} ^{3} 1 byte

```
⊥
```

Anyone who can golf this further gets a cookie!

Function submission which takes reversed coefficients as right argument and $x$ as left argument.

-8 bytes from dzaima and rak1507(APL Orchard).

-2 bytes from Adám.

Uses a mixed base conversion.

#### 0 comments

#
Japt `-x`

, ~~6~~ 5 bytes

```
Ë*VpE
```

```
Ë*VpE :Implicit input of array U and float V
Ë :Map each element D at 0-based index E
* : Multiply D by
VpE : V raised to the power of E
:Implicit output of sum of resulting array
```

#### 2 comments

Hey, welcome :D I knew there were a few Japt tricks I still didn't know about...

Turns out I was slightly overthinking it, @Quintec; a simple map does the trick.

#
Vyxal, ~~6~~, ~~5~~, 4 bytes

```
Źe*∑
```

Takes input in the format `coeffs, x`

## Explained

```
Źe*∑
Ź # Generate range [0, len(coeffs))
e # Calculate x ** [0, len(coeffs) (vectorising)
* # Multiply the coefficients by the exponated x's. The lists are extended with 0s to be the same length
∑ # Sum that list and output
```

#### 0 comments

# Raku, 19 bytes

```
(*Z*(*X**0..*)).sum
```

Is it concerning that my solution is over 30% asterisks?

### Explanation

```
( ).sum # Get the sum of
*Z*( ) # The input list zip multiplied by
*X** # The second input to the power of
0..* # 0 to infinity
```

An alternate curried solution for 19 bytes is:

```
{*.reduce(*×$_+*)}
```

#### 0 comments

# Haskell, 20 bytes

```
f x=foldl((+).(x*))0
```

Takes input coefficients from highest degree to lowest.

**21 bytes**

```
x%(h:t)=h+x*x%t
x%_=0
```

#### 0 comments

# Ruby, 50 bytes

```
def f(k,x)k.length>1?k[0]+f(k[1..-1],x)*x:k[-1]end
```

This uses the Horner's method recursively, because I think it'll be slightly shorter than using a loop or builtin array functions.

Also, this is my first post on this website ... er my first real attempt at golfing something in Ruby, so please feel free to suggest ways to shorten my solution.

#### 0 comments

# Jelly, 1 byte

```
ḅ
```

Essentially just Razetime's APL answer, except in that `ḅ`

vectorizes rather than carrying out mixed base conversion--irrelevant if, as is the case here, the provided base is scalar. Takes a reversed coefficient list on the left and $x$ on the right.

## 2 comments

"Input can be in any format of choice, as long as it is a list of numbers" ― does this mean we can take the list in reverse order? — Adám 5 months ago

@Adam Effectively yes, and i don't feel like going back to change that to "correctly ordered list of numbers", so go for it — moony 5 months ago