linalg: return out array for .toArray, create symmetric mat3

src/mol-math/linear-algebra/3d/mat3.ts

@@ -72,6 +72,7 @@ namespace Mat3 {
         out[offset + 6] = a[6];
         out[offset + 7] = a[7];
         out[offset + 8] = a[8];
+        return out;
     }
 
     export function fromArray(a: Mat3, array: NumberArray, offset: number) {
@@ -220,6 +221,44 @@ namespace Mat3 {
         return out;
     }
 
+    export function symmtricFromUpper(out: Mat3, a: Mat3) {
+        if (out === a) {
+            out[3] = a[1];
+            out[6] = a[2];
+            out[7] = a[5];
+        } else {
+            out[0] = a[0];
+            out[1] = a[1];
+            out[2] = a[2];
+            out[3] = a[1];
+            out[4] = a[4];
+            out[5] = a[5];
+            out[6] = a[2];
+            out[7] = a[5];
+            out[8] = a[8];
+        }
+        return out;
+    }
+
+    export function symmtricFromLower(out: Mat3, a: Mat3) {
+        if (out === a) {
+            out[1] = a[3];
+            out[2] = a[6];
+            out[5] = a[7];
+        } else {
+            out[0] = a[0];
+            out[1] = a[3];
+            out[2] = a[6];
+            out[3] = a[3];
+            out[4] = a[4];
+            out[5] = a[7];
+            out[6] = a[6];
+            out[7] = a[7];
+            out[8] = a[8];
+        }
+        return out;
+    }
+
     export function determinant(a: Mat3) {
         const a00 = a[0], a01 = a[1], a02 = a[2];
         const a10 = a[3], a11 = a[4], a12 = a[5];

src/mol-math/linear-algebra/3d/mat4.ts

@@ -141,6 +141,7 @@ namespace Mat4 {
         out[offset + 13] = a[13];
         out[offset + 14] = a[14];
         out[offset + 15] = a[15];
+        return out;
     }
 
     export function fromArray(a: Mat4, array: NumberArray, offset: number) {

src/mol-math/linear-algebra/3d/quat.ts

@@ -318,6 +318,7 @@ namespace Quat {
         out[offset + 1] = a[1];
         out[offset + 2] = a[2];
         out[offset + 3] = a[3];
+        return out;
     }
 
     export function fromArray(a: Quat, array: NumberArray, offset: number) {

src/mol-math/linear-algebra/3d/vec2.ts

@@ -53,6 +53,7 @@ namespace Vec2 {
     export function toArray(a: Vec2, out: NumberArray, offset: number) {
         out[offset + 0] = a[0];
         out[offset + 1] = a[1];
+        return out;
     }
 
     export function fromArray(a: Vec2, array: NumberArray, offset: number) {

src/mol-math/linear-algebra/3d/vec3.ts

@@ -73,6 +73,7 @@ namespace Vec3 {
         out[offset + 0] = v[0]
         out[offset + 1] = v[1]
         out[offset + 2] = v[2]
+        return out
     }
 
     export function create(x: number, y: number, z: number): Vec3 {

src/mol-math/linear-algebra/3d/vec4.ts

@@ -62,6 +62,7 @@ namespace Vec4 {
         out[offset + 1] = a[1];
         out[offset + 2] = a[2];
         out[offset + 3] = a[3];
+        return out;
     }
 
     export function fromArray(a: Vec4, array: NumberArray, offset: number) {