# compiling problems with new versions

Hi, I've been developing a project on my university's computers (which unfortunately run a 4.7.1 version) and on the sagenb.org site, and everything went fine. But as soon as I tried to run the project on cloud.sagemath I ran into problems (like a "keyerror 0" message). After some work I think that these problems are somehow due to the .ngens() function, so I'd like to know if there are some known issues regarding versions update and/or with this particular function. thanks

I think we need some more details, this is pretty vague. We try pretty hard to maintain backwards compatibility but there may be something here. Is there a minimal case you can provide, and edit your question to incorporate?

I tried to cut of the project a minimal case, but after some more debugging it seems that the problem is that the .homology() function of an acyclic chain complex is an empty dictionary, while according to the documentation it should be a dictionary containing the value 0 in the appropriate degrees. In other terms, i would like the output of: sage: D = ChainComplex({0: identity_matrix(ZZ, 4), 4: identity_matrix(ZZ, 30)}) sage: D.homology()

to be {0: 0, 1: 0, 4: 0, 5: 0}, while on cloud.sagemath it gives back just {}

I can confirm this is a bug in SMC. I have no problems with old or new Sage outside of the cloud, but it happens there.

Maybe this is caused by SMC having an optional package installed, which might change the semantics. When I try with a clean build of Sage (without the optional packages installed) then it works as you expect. So possibly this doesn't have anything to do specifically with SMC, but with some optional package. Here's a worksheet, btw: https://cloud.sagemath.com/projects/4...

Thanks for the quick clarification! is there any possible known quick way to bypass the problem (I guess I could try to fix my problem somehow, but I would not like to create more mess if it is not necessary)