matrix initialization

[safe tapir]

const std = @import("std");
const math = std.math;
const cos = math.cos;
const sin = math.sin;
const MatrixError = error{IncompatibleDimensions};
const Point3 = struct {
    data: [3]f64,
    fn x(self: *Point3) f64 {
        return self.data[0];
    }
    fn y(self: *Point3) f64 {
        return self.data[1];
    }
    fn z(self: *Point3) f64 {
        return self.data[2];
    }
};
const Matrix = struct {
    rows: usize,
    cols: usize,
    data: [][]f64,
    fn mul(self: *Matrix, other: *Matrix) *Matrix {
        if (self.cols != other.rows) {
            return MatrixError.IncompatibleDimensions;
        }
        const rows = self.rows;
        const columns = other.cols;
        const data = std.heap.page_allocator.Allocator(f64).malloc(rows * columns);
        var sum: f64 = undefined;
        for (0..rows) |i| {
            for (0..columns) |j| {
                sum = 0;
                for (0..self.cols) |k| {
                    sum += self.data[i][k] * other.data[k][j];
                }
                data[i * columns + j] = sum;
            }
        }
        return Matrix{ .rows = rows, .cols = columns, .data = data };
    }
};
pub fn main() !void {
    const dX: f64 = 5;
    const dY: f64 = 3;
    const angle: f64 = 45.0;

    var translation1: Matrix = Matrix{
        .rows = 3,
        .cols = 3,
        .data = [3][3]f64{
            [_]f64{ 1.0, 0.0, 0.0 },
            [_]f64{ 0.0, 1.0, 0.0 },
            [_]f64{ -dX, -dY, 1.0 },
        },
    };
    var rotation: Matrix = Matrix{
        .rows = 3,
        .cols = 3,
        .data = [3][3]f64{
            [_]f64{ cos(angle), sin(angle), 0.0 },
            [_]f64{ -sin(angle), cos(angle), 0.0 },
            [_]f64{ 0.0, 0.0, 1.0 },
        },
    };
    const data = translation1.mul(&rotation);
    std.debug.print("{} ", .{data});
}

what's wrong with the way I am trying to initialize these matrices?

[river tree]

you defined the matrix's .data field to be of type [][]f64, but you're trying to initialise it with [3][3]f64.

arrays and slices are not the same thing!

also, the return type of Matrix.mul is declared to be *Matrix, but you're trying to return a Matrix

[safe tapir]

I haven't gotten to noticing taht error yet because this hasn't compiled but thank you, I'll try this out now and report back 😄

I guess it's time to learn how allocators work :DDD

[river tree]

good luck with that, indeed you should probably use some allocators here

if you're coming from C allocators might be somewhat confusing, because there is no global malloc and free

just create a question thread if you don't understand something