Balandin, V. Golubeva, N. Approximate Matrices for Modeling the Focusing of the Undulator Periods and Undulator End Fields JACoW Geneva, Switzerland 978-3-95450-182-3 10.18429/JACoW-IPAC2017-MOPIK069 English 686-688 MOPIK069 undulator focusing betatron dipole laser Contribution to a conference proceedings 2017 2017-05 http://dx.doi.org/10.18429/JACoW-IPAC2017-MOPIK069 http://jacow.org/ipac2017/papers/mopik069.pdf We describe procedure for constructing approximate matrices for modeling the focusing of the undulator periods and undulator end fields and discuss applicability of these matrices to the European XFEL undulators.