float ex(float r; float theta)
{
    return cos(theta) * r; 
}
float ey(float r; float theta)
{
    return sin(theta) * r; 
}

// Z = x + yi;
// Z*Z = (x^2 - y^2) + (2xy)*i;

float real = @P.x* @P.x - @P.y*@P.y;
float img  = 2 * @P.x * @P.y;
float r = sqrt(real * real + img*img);
float theta = atan2(img,real);

@P.x = ex(r , theta);
@P.y = ey(r , theta);