Regarding signed dihedral angle doubt

In summary, the conversation discusses calculating the Phi Psi angles or dihedral angle between two planes using the formula cos(theta)=(A.B/|A||B|). However, the result may have a positive or negative sign and the individual is seeking help on how to obtain the desired negative sign for their result. They also mention that the cosine function does not consider the sign and can be used interchangeably for positive and negative values.
  • #1
sureshjrf
1
0
Hi to all..
I am doing Phd in bioinformatics, having little knowledge abt maths..
I have calculated Phi Psi angles(dihedral angle)between two planes...
But the thing is i didnt get proper sign for my result(may be + or -).
I used following formulae for calculate the dihedral angle between two planes...
cos(theta)=(A.B/|A||B|)

any one help me how can i get the signed values for my result..

my program value..
theta=cos inverse of (-0.717563607965311)
theta=135.9,

But i need the result as -135.9

tanks in advance...
 
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  • #2
Welcome to PF!

sureshjrf said:
I have calculated Phi Psi angles(dihedral angle)between two planes...
But the thing is i didnt get proper sign for my result(may be + or -).
I used following formulae for calculate the dihedral angle between two planes...
cos(theta)=(A.B/|A||B|)
…
my program value..
theta=cos inverse of (-0.717563607965311)
theta=135.9,

But i need the result as -135.9

Hi sureshjrf! Welcome to PF! :smile:

Cos doesn't care :rolleyes: about the sign …

cos(x) = cos(-x).
​

So cos(135.9) = cos(-135.9). :wink:
 

Related to Regarding signed dihedral angle doubt

1. What is a signed dihedral angle?

A signed dihedral angle is a measurement of the angle between two planes in three-dimensional space. It takes into account the direction of rotation between the planes, resulting in a positive or negative value.

2. How is a signed dihedral angle calculated?

A signed dihedral angle can be calculated using the dot product and cross product of the vectors that define the two planes. It can also be calculated using the arccosine function.

3. What is the significance of signed dihedral angles in science?

Signed dihedral angles are important in various fields of science, such as chemistry, physics, and engineering. They are used to determine the spatial orientation of molecules, analyze crystal structures, and design complex structures that require precise angles.

4. Can a signed dihedral angle be negative?

Yes, a signed dihedral angle can be negative if the rotation between the planes is in the opposite direction of a positive angle. This is often denoted by a minus sign before the angle value.

5. How do signed dihedral angles differ from regular dihedral angles?

Regular dihedral angles only measure the magnitude of the angle between two planes, while signed dihedral angles take into account the direction of rotation between the planes. This results in a more precise measurement of the angle in three-dimensional space.

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