How to draw a circle in a matrix like this?

I came across matrices like this in a book. Can I create this using pure latex commands or do I need to using something like Photoshop for help?

enter image description here

Update: I've created the equation without circle like this:

documentclass[a4paper,12pt,hidelinks]article usepackagemathtools begindocument titleTitle of the doc authorme datetoday maketitle sectionExample beginequation* beginvmatrix*[c] a_11 & a_12 & cdots & a_1n \ & a_22 & cdots & a_2n \ && ddots & vdots \ &&& a_nn endvmatrix* = beginvmatrix*[c] a_11 &&& \ a_21 & a_22 && \ vdots & vdots & ddots & \ a_n1 & a_n2 & cdots & a_nn endvmatrix* = a_11a_22 dots a_nn endequation* enddocument

enter image description here

Welcome to TeX.SE! You certainly do not need photoshop for this. Could you please provide us with the code for the matrices without the "circle"?

– marmot
Sep 12 '18 at 13:37

OK, yes, let me do it and update the question. I just learned latex a few hours ago and this is a good chance to practice :)

– Ogrish Man
Sep 12 '18 at 13:39

The solution has been written long time ago here.

– The Inventor of God
Sep 12 '18 at 13:47

2 Answers
2

Run with xelatex

xelatex

documentclassarticle usepackageamsmath usepackagepstricks begindocument [ beginvmatrix a_11 & a_12 & cdots & a_1n \ & a_22 & cdots & a_2n \ psellipse[rot=45](0.5,0)(0.3,0.6) & & ddots & vdots \ & & & a_nn endvmatrix = beginvmatrix a_11 & & & \ a_21 & a_22 & & psellipse[rot=45](-0.5,0.1)(0.3,0.6) \ vdots & vdots & ddots & \ a_n1 & a_n1 & cdots & a_nn endvmatrix = a_11, a_22cdots a_nn ] enddocument

enter image description here

and the same with package tikz

tikz

[ beginvmatrix a_11 & a_12 & cdots & a_1n \ & a_22 & cdots & a_2n \ tikz[overlay]draw (0.5,0) circle [x radius=3mm,y radius=6mm,rotate=45]; & & ddots & vdots \ & & & a_nn endvmatrix = beginvmatrix a_11 & & & \ a_21 & a_22 & & tikz[overlay]draw (-0.5,0.1) circle [x radius=3mm,y radius=6mm,rotate=45]; \ vdots & vdots & ddots & \ a_n1 & a_n1 & cdots & a_nn endvmatrix = a_11, a_22cdots a_nn ]

Why xelatex? I get the result also with "normal" latex.

– campa
Sep 12 '18 at 15:00

xelatex

latex

With latex yes, but not with pdflatex.

– Herbert
Sep 12 '18 at 15:09

latex

pdflatex

Here is a possible way to do it with tikzmark. (UPDATE: Rotation angles of the ellipses are no longer hard coded.)

documentclass[a4paper,12pt,hidelinks]article usepackagemathtools usepackagetikz usetikzlibrarytikzmark,fit,shapes.geometric,calc begindocument titleTitle of the doc authorme datetoday maketitle sectionExample beginequation* beginvmatrix*[c] a_11 & a_12 & cdots & a_1n \ & a_22 & cdots & a_2n \ tikzmarkm1&& ddots & vdots \ &tikzmarkm2&& a_nn endvmatrix* = beginvmatrix*[c] a_11 &&tikzmarkm3& \ a_21 & a_22 &&tikzmarkm4 \ vdots & vdots & ddots & \ a_n1 & a_n2 & cdots & a_nn endvmatrix* = a_11a_22 dots a_nn endequation* begintikzpicture[overlay,remember picture] path let p1=($(pic cs:m2)-(pic cs:m1)$),n1=atan2(y1,x1) in node[ellipse,fit=(pic cs:m1)(pic cs:m2),draw,rotate fit=n1,inner sep=0pt, yshift=4pt]; path let p1=($(pic cs:m4)-(pic cs:m3)$),n1=atan2(y1,x1) in node[ellipse,fit=(pic cs:m3)(pic cs:m4),draw,rotate fit=n1,inner sep=0pt]; endtikzpicture enddocument

enter image description here

Thanks for contributing an answer to TeX - LaTeX Stack Exchange!

But avoid …

To learn more, see our tips on writing great answers.

Required, but never shown

By clicking "Post Your Answer", you acknowledge that you have read our updated terms of service, privacy policy and cookie policy, and that your continued use of the website is subject to these policies.

搜尋此網誌

Dfyjkt