Consider a random matrix H:Rn⟶Rm\documentclass[12pt]{minimal}
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\begin{document}$$H:{\mathbb {R}}^{n}\longrightarrow {\mathbb {R}}^{m}$$\end{document}. Let D≥2\documentclass[12pt]{minimal}
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\begin{document}$$D\ge 2$$\end{document} and let {Wl}l=1p\documentclass[12pt]{minimal}
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\begin{document}$$\{W_l\}_{l=1}^{p}$$\end{document} be a set of k\documentclass[12pt]{minimal}
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\begin{document}$$k$$\end{document}-dimensional affine subspaces of Rn\documentclass[12pt]{minimal}
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\begin{document}$${\mathbb {R}}^{n}$$\end{document}. We ask what is the probability that for all 1≤l≤p\documentclass[12pt]{minimal}
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\begin{document}$$1\le l\le p$$\end{document} and x,y∈Wl\documentclass[12pt]{minimal}
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\begin{document}$$x,y\in W_l$$\end{document}, ‖x-y‖2≤‖Hx-Hy‖2≤D‖x-y‖2.\documentclass[12pt]{minimal}
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\begin{document}$$\begin{aligned} \Vert x-y\Vert _2\le \Vert Hx-Hy\Vert _2\le D\Vert x-y\Vert _2. \end{aligned}$$\end{document}We show that for m=O(k+lnplnD)\documentclass[12pt]{minimal}
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\begin{document}$$m=O\big (k+\frac{\ln {p}}{\ln {D}}\big )$$\end{document} and a variety of different classes of random matrices H\documentclass[12pt]{minimal}
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\begin{document}$$H$$\end{document}, which include the class of Gaussian matrices, existence is assured and the probability is very high. The estimate on m\documentclass[12pt]{minimal}
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\begin{document}$$m$$\end{document} is tight in terms of k,p,D\documentclass[12pt]{minimal}
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\begin{document}$$k,p,D$$\end{document}.
