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Keywords: G4RotationMatrix, round-off errors
Forum: Geometry
Re: Question G4RotationMatrix defined by specifying actual Matrix gives warning (Ioannis Sechopoulos)
Date: 25 Oct, 2006
From: Gabriele Cosmo <Gabriele Cosmo>

Hi Ioannis,

> Hello, I am defining a G4RotationMatrix to rotate a volume using:
>
> A = new G4RotationMatrix(G4ThreeVector(alpha1, alpha2, alpha3),
>                              G4ThreeVector(beta1, beta2, beta3),
>                              G4ThreeVector(gamma1, gamma2, gamma3));
> which specifically defines the rotation matrix according to the header file. alpha1,
> alpha2, etc are all floats. I get the following warnings:
>
> ZMxpvNotOrthogonal:
>
> ZMxpvNotOrthogonal: col's X and Y supplied for Rotation are not close to orthogonal
> at line 86 in file RotationC.cc ZMxpvNotOrthogonal:
> ...
> I checked, and the rotation matrix is not exactly orthogonal because transpose(A)*A
> gives me almost the identity matrix but with small round off errors in the fourth
> decimal place. Will I face a problem if I still use this RotationMatrix? The volume
> appears fine in graphical output, but I am concerned that maybe the Navigator wil
> l run into trouble.

since Geant4 runs inherently in double precision, I would suggest you to correct
the way you define your rotation matrix, by checking the types and way you compute
the input parameters to the transformation and satisfy the orthogonality
preconditions.

Cheesr, Gabriele

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