Re: C codes for dihedral angle

[Renxiao Wang <renxiao()at()chem.ucla.edu>]

 Dear rajarshi,
 I think you have already been overwhelmed by unrelevent answers. Here is
 exactly what you want:
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 float Torsion_Angle(float p1[3], float p2[3], float p3[3], float p4[3])  {
         int i;
         float angle;
         float v12[3],v23[3],v34[3],v1[3],v2[3],v3[3];
         for(i=0;i<=2;i++)
                 {
                  v12[i]=p2[i]-p1[i];
                  v23[i]=p3[i]-p2[i];
                  v34[i]=p4[i]-p3[i];
                 }
         Cross_Multiply(v12,v23,v1);
         Cross_Multiply(v23,v34,v2);
         angle=Angle_Of_Two_Vectors(v1,v2);
         Cross_Multiply(v1,v2,v3);
         if((v23[0]/v3[0]>0)||(v23[1]/v3[1]>0)||(v23[2]/v3[2])>0) return
 angle;
         else return -angle;  }
 void Cross_Multiply(float v1[3], float v2[3], float result[3])  {
         result[0]=v1[1]*v2[2]-v2[1]*v1[2];
         result[1]=v1[2]*v2[0]-v2[2]*v1[0];
         result[2]=v1[0]*v2[1]-v2[0]*v1[1];
         return;  }
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 This is cut from my program LigBuilder. Hope it helps.
 Best wishes,
 Arthur
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 | Dr. Renxiao Wang                                                     |
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 | Department of Chemistry and Biochemistry | 3281 Sawtelle Blvd. #104  |
 | University of California Los Angeles     | Los Angeles, CA90066      |
 | Los Angeles, CA 90024                    | U.S.A                     |
 | Phone: 310-8250269 (Lab)                 | Phone: 310-3904638 (Home) |
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 | E-mail: renxiao()at()chem.ucla.edu                                        |
 | WWW: http://zimbu.chem.ucla.edu/~arthur/
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