# vtkArrayCalculator constant vector operation

**URL:** https://discourse.vtk.org/t/vtkarraycalculator-constant-vector-operation/3807
**Category:** Support
**Created:** [July 20, 2020, 6:07am UTC](https://discourse.vtk.org/t/vtkarraycalculator-constant-vector-operation/3807 "2020-07-20T06:07:44Z")
**Posts on this page:** 1
**Page:** 1

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### Author: ![tkeskita](https://discourse.vtk.org/user_avatar/discourse.vtk.org/tkeskita/32/1757_2.png) [@tkeskita](https://discourse.vtk.org/u/tkeskita)
#### Post date: [July 20, 2020, 6:07am UTC](https://discourse.vtk.org/t/vtkarraycalculator-constant-vector-operation/3807/1 "2020-07-20T06:07:44Z")

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A simple Python `vtkArrayCalculator` question: how can I specify a constant vector `c` in `SetFunction` so that I can do vector operation like `U + c` for an existing vector field `U`? I introduce `U` using `AddVectorArrayName("U")`.

**Edit:** I found out one way: `U + 0.1*iHat + 0.2*jHat + 0.3*kHat`, is there another way?