# Why there is a tensor 4 data for several components pde?

Asked by
Qian Han

Hi,

Several components pde has a general form likes:

(A_{ijkl}*u[k],l),j ..... = ....

I am confused about the tensor 4 data object A:

Einstein notation does not include the index i.

Does this mean, the equation is along the i direction ?

For example, there is a 2d static equilibrium continuum

At axis x, pde is: (A_{xjkl}*u[k],l),j we only sum terms j, k, l.

At axis y, pde looks like pde for x just replace x by y.

Finally, sum the two eqs of x and y in order to get the general pde form as listed in user guide of esys-escript.

Any reply will be grateful!

Thank you!

Best regards,

Qian Han

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