        case .Float:
            let ret = math_vv_by_vForce(mfarray, vvcosf)
            ret.mfdata._mftype = .Float
            return ret
        case .Double:
            let ret = math_vv_by_vForce(mfarray, vvcos)
            ret.mfdata._mftype = .Double
            return ret
        }
    }
    /**
       Calculate the arccos for all elements
       - parameters:
            - mfarray: mfarray