Slightly buggy Matrix class for wOOP

--todo
--implement http://www.mathsisfun.com/algebra/matrix-inverse-minors-cofactors-adjugate.html in a matrix class
--implement matrix multiplication in same class
--implement points iterator
--implement size function

local function dot(v1,v2)
    print(#v1,#v2)
    local n=0
    for i,v in ipairs(v1) do
        n=n+v*v2[i]
    end
    return n
end

class "matrix"
{
    __settings=
    {
        new=
        function(a,b,...)
            if type(a)=="number" and type(b)=="number" then
                local newmatrix={}
                local defaultval={...}
                defaultval=defaultval[1]
                for y=1,b do
                    newmatrix[y]={}
                    for x=1,a do
                        newmatrix[y][x]=defaultval
                    end
                end
                return {matrix=newmatrix}
            else
                local mat={}
                if not b then
                    if type(a[1])=="table" then
                        mat=a
                    else
                        mat={a}
                    end
                else
                    mat={a,b,...}
                end
                return {matrix=mat}
            end
        end,
        mt=
        {
            __call=
            function(self,x,y,v)
                if self.matrix[y] and self.matrix[y][x] then
                    local val=self.matrix[y][x]
                    if v then
                        self.matrix[y][x]=v
                    end
                    return val
                end
            end,

            __tostring=
            function(self)
                local prevy=1
                local str="Matrix:\n"
                for x,y,v in self.points() do
                    local attach=", "
                    if x==1 and y==1 then attach="" end
                    if y>prevy then
                        prevy=y
                        attach="\n"
                    end
                    str=str..attach..tostring(v)
                end
                return str
            end
        }
    },
    scalarmultiply=
    function(num)
        local result={}
        local X,Y=self.size()
        for y=1,Y do
            result[y]={}
            for x=1,X do
                result[y][x]=self(x,y)*num
            end
        end
        return matrix(result)
    end,
    matrixmultiply= --issue is here k
    function(other)
        local x1,y1=self.size()
        local x2,y2=other.size()
        if y1==x2 then --same inner dimensions
            local result=matrix(x1,y2,0) --outers
            for y=1,y2 do
                for x=1,x1 do
                    local sum=0
                    for i=1,x2 do
                        local v=x
                        if not other(v,i) then
                            v=1
                        end
                        sum=sum+self(i,x)*(other(x,i) or other(1,i))
                    end
                    result(x,y,sum)
                end
            end
            return result
        else
            error("Inner dimensions must match in matrix multiplication!")
        end
    end,
    size=
    function()
        return #self.matrix,#self.matrix[1]
    end,
    points=
    function()
        local posY,posX=1,0
        return function()
            posX=posX+1
            if not self(posX,posY) then
                posY=posY+1
                if self.matrix[posY] then
                    posX=1
                else
                    return nil
                end
            end
            return posX,posY,self(posX,posY)
        end
    end,
    det=
    function()
        local sizex,sizey=self.size()
        if sizex==sizey and sizex==2 then
            return self(1,1)*self(2,2)-self(1,2)*self(2,1)
        end
        if sizex==sizey then
            local det=0

            for badX=1,sizex do
                local mat={}
                for y=1,sizey do
                    if y~=1 then
                        mat[y-1]={}
                        for x=1,sizex do
                            if x~=badX then
                                mat[#mat][#mat[#mat]+1]=self(x,y)
                            end
                        end
                    end
                end
                local newmat=matrix(mat)
                det=det+(badX%2==1 and -1 or 1)*newmat.det()*self(badX,1)
            end
            return det
        end
    end,
    inv=
    function()
        local SELFDET=self.det()
        local sizex,sizey=self.size()
        if SELFDET==0 then
            return "Cannot get inverse of this matrix - det 0"
        end
        if sizex==2 and sizey==2 then
            return matrix({self(2,2),-self(2,1)},{-self(1,2),self(1,1)})
        end
        if sizex==sizey then
            local minors={}
            for badY=1,sizey do
                minors[badY]={}
                for badX=1,sizex do
                    local mat={}
                    for y,row in pairs(self.matrix) do
                        local clone={}
                        for i,v in pairs(row) do
                            clone[i]=v
                        end
                        table.remove(clone,badX)
                        mat[#mat+1]=clone
                    end
                    table.remove(mat,badY)
                    minors[badY][badX]=matrix(mat).det()
                end
            end
            for val=1,sizex do
                local odd=val%2==1
                local row=minors[val]
                for x,val in ipairs(row) do
                    local odd2=x%2==1
                    if odd and odd2 then
                        row[x]=-val
                    elseif not odd and not odd2 then
                        row[x]=-val
                    end
                end
            end
            local MINORSMAT=matrix(minors)
            for x,y,v in MINORSMAT.points() do
                if x>y then
                    MINORSMAT(x,y,MINORSMAT(y,x,MINORSMAT(x,y)))
                end
            end
            return MINORSMAT.scalarmultiply(SELFDET^-1)
        end
    end
}