new file mode 100644
--- /dev/null
+++ b/scripts/quaternion/qtransv.m
@@ -0,0 +1,23 @@
+function vi = qtransv(vb,qib)
+# function vi = qtransv(vb,q)
+# transform the 3-D vector v by the unit quaternion q;
+# v = [w x y z], q = transformation quaternion
+# returns vi = column vector
+#    vi = (2*real(q)^2 - 1)*vb + 2*imag(q)*(imag(q)'*vb) 
+#      + 2*real(q)*cross(imag(q),vb)
+#    where imag(q) is a column vector of length 3.
+
+if(!is_vector(vb) | length(vb) != 3)
+  error(sprintf("qtransv: v(%d,%d) must be a 3-D vector",rows(vb),columns(vb)))
+elseif(!is_vector(qib) | length(qib) != 4)
+  error(sprintf("qtransv: q(%d,%d) must be a quaternion",rows(qib),columns(qib)))
+elseif(max(abs(imag(vb))) + max(abs(imag(qib))) != 0)
+  vb
+  qib
+  error("qtransv: input values must be real.");
+endif
+
+qr = qib(4);  qimag = vec(qib(1:3));   vb = vec(vb);
+vi = (2*qr^2 - 1)*vb + 2*qimag*(qimag'*vb) + 2*qr*cross(qimag,vb);
+
+endfunction