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I want to create an system of equation in LyX, like this:

equation

Can anyone help me?

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    The answer can be found directly at my previous question, there is a step-by-step procedure that will keep you from writing tedious ERT directly on LyX. Oh, by the way, let me know if I'll have to add an answer here (just for coherence). – TheVal Oct 5 '13 at 9:59
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You can try the systeme package.

enter image description here

\documentclass{article}
\usepackage{amsmath}
\usepackage{systeme}

\begin{document}

\systeme{
x_1  -  x_3  =  0.2,
-\dfrac{1}{2} x_1  +  x_2  -  \dfrac{1}{4} x_3  =  -1.425,
x_1  -  \dfrac{1}{2} x_2  +  x_3  =  2
}

\end{document} 

(I have found it...) Issuing the command

\syslineskipcoeff{2}

before the \systeme makes it look better (IMHO):

enter image description here

| improve this answer | |
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    LyX is high-level processor, we should try to avoid explicit TeX whenever possible. – juliohm Oct 5 '13 at 14:47
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    @juliohm LyX may be “high level”, but you don't obtain the same result with the way you suggest in your answer, do you? – egreg Oct 5 '13 at 14:49
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    @downvoter is your down vote because it is not the best way to go in LyX? I'm not a LyX expert, but please explain why you've downvoted. – karlkoeller Oct 5 '13 at 15:37
2

In math display mode, you can just type in the first equation, then press Ctrl+Enter, type in the second, and so on.

If alignment of columns is important, you do the same procedure but within an appropriate environment such as Insert -> Math -> Aligned Environment.

| improve this answer | |
  • I think the OP wants a proper alignment inside every inlined equation that belongs to the system. In order to achieve this a column separation macro could be defined in the preamble, (i.e. modifying the array envir.); I'm saying this because the result for Ctrl+Enter won't re-create the system wanted. – TheVal Oct 5 '13 at 15:56
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    I'm 99.99% sure that it is you that downvoted my answer. I agree that it is not the best way to go in LyX. But really do you think that your answer is better? BTW: I won't downvote your answer, anyway... – karlkoeller Oct 5 '13 at 16:45
  • @karlkoeller, how is your answer specific to LyX? It's for sure a good answer. – juliohm Oct 5 '13 at 23:45
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    @AndreaL., my answer is targeted to the specific little system of equations illustrated in the question, I should have designed a better solution though. It's just a trade-off between how much you bother with alignment or not. LyX also has direct insertion for array,aligned,cases,... that follows the same idea with Ctrl+Enter. I'll update the answer. – juliohm Oct 5 '13 at 23:57
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    @juliohm Please, can you show the result you're getting? Otherwise your answer can't help the OP. Anyway, I don't think you can easily get the same result with your suggestion as with systeme. – egreg Oct 6 '13 at 0:19

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