Skip to main content

bugs - Return value of Import "MX" when file was saved with newer version


I just detected that Mathematica 10.4.1 on Windows will just quietly return Null when I try to Import an .mx file I exported with version 11.1.1. I understand and know that .mx files that were generated with newer versions will generally not load with older versions. Up to now I thought (and I believe I have seen that for older verions) it would give some message and return $Failed, but obviously this is not the case here. As often, the documentation page for the MX format is not giving detailed information about that specific case.


My question is whether that is the expected behavior and whether there is some documentation about that or that would be something to report to WRI...



Answer



This is indeed a bug. A careless tweak was made to the format, so that MX files created by Version 11.1 or newer aren't even recognized as MX files by pre-11.1.0 versions. So Get is succeeding, reading the binary file as text and returning Null because it encounters a zero byte, interpreted as end of file, early on. If for some reason it is important to you that old versions properly recognize and reject newer MX files, you can use the program below after you DumpSave to tweak the MX file. This version will be loaded by V11.1+, and properly rejected as too new by older versions.


On the plus side, one thing we did in the forth coming 11.2 is improve cross-version compatibility of MX files. So, unless a new feature forces an incompatible change in the format, 11.2 will be able to read MX files from later versions. (Obviously, new features won't work in an older kernel).


newHeader = {40, 42, 84, 104, 105, 115, 32, 105, 115, 32, 97, 32, 77, 
   97, 116, 104, 101, 109, 97, 116, 105, 99, 97, 32, 98, 105, 110, 97,
    114, 121, 32, 100, 117, 109, 112, 32, 102, 105, 108, 101, 46, 32, 
   73, 116, 32, 99, 97, 110, 32, 98, 101, 32, 108, 111, 97, 100, 101, 

   100, 32, 119, 105, 116, 104, 32, 71, 101, 116, 46, 42, 41};

newFooter = {40, 42, 69, 110, 100, 32, 111, 102, 32, 77, 97, 116, 104,
    101, 109, 97, 116, 105, 99, 97, 32, 98, 105, 110, 97, 114, 121, 
   32, 100, 117, 109, 112, 32, 102, 105, 108, 101, 42, 41, 0};

fixUp111PlusMX[file_] := With[{bytes = BinaryReadList[file], path = AbsoluteFileName[file]},
   BinaryWrite[path, 
   Join[newHeader, Take[bytes, {79, -49}], newFooter]];
   Close[path]

]

Comments

Post a Comment

Popular posts from this blog

functions - Get leading series expansion term?

Given a function f[x] , I would like to have a function leadingSeries that returns just the leading term in the series around x=0 . For example: leadingSeries[(1/x + 2)/(4 + 1/x^2 + x)] x and leadingSeries[(1/x + 2 + (1 - 1/x^3)/4)/(4 + x)] -(1/(16 x^3)) Is there such a function in Mathematica? Or maybe one can implement it efficiently? EDIT I finally went with the following implementation, based on Carl Woll 's answer: lds[ex_,x_]:=( (ex/.x->(x+O[x]^2))/.SeriesData[U_,Z_,L_List,Mi_,Ma_,De_]:>SeriesData[U,Z,{L[[1]]},Mi,Mi+1,De]//Quiet//Normal) The advantage is, that this one also properly works with functions whose leading term is a constant: lds[Exp[x],x] 1 Answer Update 1 Updated to eliminate SeriesData and to not return additional terms Perhaps you could use: leadingSeries[expr_, x_] := Normal[expr /. x->(x+O[x]^2) /. a_List :> Take[a, 1]] Then for your examples: leadingSeries[(1/x + 2)/(4 + 1/x^2 + x), x] leadingSeries[Exp[x], x] leadingSeries[(1/x + 2 + (1 - 1/x...
Post a Comment
Read more

How to thread a list

I have data in format data = {{a1, a2}, {b1, b2}, {c1, c2}, {d1, d2}} Tableform: I want to thread it to : tdata = {{{a1, b1}, {a2, b2}}, {{a1, c1}, {a2, c2}}, {{a1, d1}, {a2, d2}}} Tableform: And I would like to do better then pseudofunction[n_] := Transpose[{data2[[1]], data2[[n]]}]; SetAttributes[pseudofunction, Listable]; Range[2, 4] // pseudofunction Here is my benchmark data, where data3 is normal sample of real data. data3 = Drop[ExcelWorkBook[[Column1 ;; Column4]], None, 1]; data2 = {a #, b #, c #, d #} & /@ Range[1, 10^5]; data = RandomReal[{0, 1}, {10^6, 4}]; Here is my benchmark code kptnw[list_] := Transpose[{Table[First@#, {Length@# - 1}], Rest@#}, {3, 1, 2}] &@list kptnw2[list_] := Transpose[{ConstantArray[First@#, Length@# - 1], Rest@#}, {3, 1, 2}] &@list OleksandrR[list_] := Flatten[Outer[List, List@First[list], Rest[list], 1], {{2}, {1, 4}}] paradox2[list_] := Partition[Riffle[list[[1]], #], 2] & /@ Drop[list, 1] RM[list_] := FoldList[Transpose[{First@li...
Post a Comment
Read more

front end - keyboard shortcut to invoke Insert new matrix

I frequently need to type in some matrices, and the menu command Insert > Table/Matrix > New... allows matrices with lines drawn between columns and rows, which is very helpful. I would like to make a keyboard shortcut for it, but cannot find the relevant frontend token command (4209405) for it. Since the FullForm[] and InputForm[] of matrices with lines drawn between rows and columns is the same as those without lines, it's hard to do this via 3rd party system-wide text expanders (e.g. autohotkey or atext on mac). How does one assign a keyboard shortcut for the menu item Insert > Table/Matrix > New... , preferably using only mathematica? Thanks! Answer In the MenuSetup.tr (for linux located in the $InstallationDirectory/SystemFiles/FrontEnd/TextResources/X/ directory), I changed the line MenuItem["&New...", "CreateGridBoxDialog"] to read MenuItem["&New...", "CreateGridBoxDialog", MenuKey["m", Modifiers-...
Post a Comment
Read more