MVPoly: add a from to increase the number of variables

mvpoly/src/monomials.rs

@@ -609,3 +609,20 @@ impl<F: PrimeField, const N: usize, const D: usize> From<F> for Sparse<F, N, D>
         result
     }
 }
+
+impl<F: PrimeField, const N: usize, const D: usize, const M: usize> From<Sparse<F, N, D>>
+    for Result<Sparse<F, M, D>, String>
+{
+    fn from(poly: Sparse<F, N, D>) -> Result<Sparse<F, M, D>, String> {
+        if M < N {
+            return Err("The number of variables must be greater than N".to_string());
+        }
+        let mut monomials = HashMap::new();
+        poly.monomials.iter().for_each(|(exponents, coeff)| {
+            let mut new_exponents = [0; M];
+            new_exponents[0..N].copy_from_slice(&exponents[0..N]);
+            monomials.insert(new_exponents, *coeff);
+        });
+        Ok(Sparse { monomials })
+    }
+}

mvpoly/tests/monomials.rs

@@ -534,3 +534,64 @@ fn test_is_multilinear() {
     let p3 = unsafe { Sparse::<Fp, 6, 4>::random(&mut rng, None) };
     assert!(!p3.is_multilinear());
 }
+
+#[test]
+fn test_increase_number_of_variables() {
+    let mut rng = o1_utils::tests::make_test_rng(None);
+    let p1: Sparse<Fp, 4, 2> = unsafe { Sparse::<Fp, 4, 2>::random(&mut rng, None) };
+
+    let p2: Result<Sparse<Fp, 5, 2>, String> = p1.into();
+    p2.unwrap();
+}
+
+#[test]
+fn test_pbt_increase_number_of_variables_with_addition() {
+    let mut rng = o1_utils::tests::make_test_rng(None);
+    let p1: Sparse<Fp, 4, 2> = unsafe { Sparse::<Fp, 4, 2>::random(&mut rng, None) };
+    let p2: Sparse<Fp, 4, 2> = unsafe { Sparse::<Fp, 4, 2>::random(&mut rng, None) };
+
+    let lhs: Sparse<Fp, 5, 2> = {
+        let p: Result<Sparse<Fp, 5, 2>, String> = (p1.clone() + p2.clone()).into();
+        p.unwrap()
+    };
+
+    let rhs: Sparse<Fp, 5, 2> = {
+        let p1: Result<Sparse<Fp, 5, 2>, String> = p1.clone().into();
+        let p2: Result<Sparse<Fp, 5, 2>, String> = p2.clone().into();
+        p1.unwrap() + p2.unwrap()
+    };
+
+    assert_eq!(lhs, rhs);
+}
+
+#[test]
+fn test_pbt_increase_number_of_variables_zero_one_cst() {
+    let mut rng = o1_utils::tests::make_test_rng(None);
+    {
+        let lhs_zero: Sparse<Fp, 5, 2> = {
+            let p: Result<Sparse<Fp, 5, 2>, String> = Sparse::<Fp, 4, 2>::zero().into();
+            p.unwrap()
+        };
+        let rhs_zero: Sparse<Fp, 5, 2> = Sparse::<Fp, 5, 2>::zero();
+        assert_eq!(lhs_zero, rhs_zero);
+    }
+
+    {
+        let lhs_one: Sparse<Fp, 5, 2> = {
+            let p: Result<Sparse<Fp, 5, 2>, String> = Sparse::<Fp, 4, 2>::one().into();
+            p.unwrap()
+        };
+        let rhs_one: Sparse<Fp, 5, 2> = Sparse::<Fp, 5, 2>::one();
+        assert_eq!(lhs_one, rhs_one);
+    }
+
+    {
+        let c = Fp::rand(&mut rng);
+        let lhs: Sparse<Fp, 5, 2> = {
+            let p: Result<Sparse<Fp, 5, 2>, String> = Sparse::<Fp, 4, 2>::from(c).into();
+            p.unwrap()
+        };
+        let rhs: Sparse<Fp, 5, 2> = Sparse::<Fp, 5, 2>::from(c);
+        assert_eq!(lhs, rhs);
+    }
+}