On Fri, Jun 24, 2016 at 6:40 AM, Prateek Gupta <prateekgidolia@gmail.com> wrote:

Hello Turhan,

I am not sure but I think this will work, you can try this...

ds = yt.load("data_file_Name")

grad = ds.add_gradient_fields(("gas","gravitational_potential"))

grad list will have a list of new field names which representing the 3 different components of the field and the magnitude of the gradient , e.g., "gravitational_potential_gradient_x" , "gravitational_potential_gradient_y" , "gravitational_potential_gradient_z" and "gravitational_potential_gradient_magnitude"

Now for getting the negative gradient of gravitational potential we can derive field as follows:

####...x-component of negative of gradient of gravitational potential...

def _GradientX(field, data)

     Gx = -1.0*data["gravitational_potential_gradient_x"]

     return Gx

yt.add_field("Gx", function=_GradientX, take_log=False, units="code length/ code time**2")

####...y-component of negative of gradient of gravitational potential...

def _GradientY(field, data)

     Gy = -1.0*data["gravitational_potential_gradient_y"]

     return Gx

yt.add_field("Gy", function=_GradientY, take_log=False, units="code length/ code time**2")

####...z-component of negative of gradient of gravitational potential...

def _GradientZ(field, data)

     Gz = -1.0*data["gravitational_potential_gradient_z"]

     return Gz

yt.add_field("Gz", function=_GradientZ, take_log=False, units="code length/ code time**2")

Otherwise you can do this also, 

grad = -1.0*ds.add_gradient_fields(("gas","gravitational_potential"))

This isn't quite right. The ds.add_gradient_fields function returns a set of field names, not a field object itself. If you want to add the negative signs to the field definition, you'll need to define some derived fields as Prateek suggested above.

 

I think this will work but this will also make the magnitude negative. But if you want to use only 3-components then this works and you can access it , e.g., data["gravitational_potential_gradient_x"] and similar for y and z component.

Please let me know if this work.

Regards

Prateek Gupta

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