[BUG] Build System Issue: make distclean Removes Required PDF Dependencies

[guntas-13]

The current Makefile build system has a critical flaw where make distclean removes PDF files that are actually required dependencies for LaTeX compilation, not just generated outputs.

Steps to Reproduce

1. Modify a shared style file (e.g., shared/styles/custom.sty)
2. Run make all in any topic directory (e.g., neural-networks/)
3. Get "Nothing to be done for 'all'" because PDFs exist and are newer than .tex files
4. Run make distclean to force rebuild
5. Run make all again
6. ERROR: Compilation fails because required *-notes.pdf files are missing

Root Cause

The distclean target indiscriminately removes all PDF files:

distclean: clean
	cd $(SLIDES_DIR) && rm -f *.pdf

This removes two different types of PDFs:

1. Generated PDFs (should be deleted): autograd.pdf, cnn.pdf, etc.
2. Source PDFs (should NOT be deleted): autograd-notes.pdf, cnn-notes.pdf, etc.

Current Affected Files

Files that include external PDF dependencies:

• neural-networks/slides/autograd.tex → autograd-notes.pdf
• neural-networks/slides/cnn.tex → cnn-notes.pdf
• neural-networks/slides/mlp.tex → mlp-notes.pdf
• neural-networks/slides/cnn-1d.tex → cnn-notes.pdf
• neural-networks/slides/next-token-prediction.tex → next-token-notes.pdf
• maths/slides/constrained-1.tex → constrained-1-notes.pdf
• maths/slides/constrained-2.tex → constrained-2-notes.pdf
• And others...

Proposed Solutions

Option 1: Smarter distclean

Only remove PDFs that correspond to existing .tex files:

distclean: clean
	cd $(SLIDES_DIR) && for tex in *.tex; do rm -f "$${tex%.tex}.pdf"; done

Option 2: Separate directories

• Move source PDFs to assets/ directory
• Update \includepdf paths accordingly
• Keep only generated PDFs in slides/

Option 3: Dependency tracking

In each of the Makefiles, instead of

# Rule to compile LaTeX to PDF
$(SLIDES_DIR)/%.pdf: $(SLIDES_DIR)/%.tex
	@echo "Compiling $< to $@"
	cd $(SLIDES_DIR) && pdflatex -interaction=nonstopmode $(notdir $<)
	cd $(SLIDES_DIR) && pdflatex -interaction=nonstopmode $(notdir $<)

Add dependency tracking for style files:

# Rule to compile LaTeX to PDF
$(SLIDES_DIR)/%.pdf: $(SLIDES_DIR)/%.tex $(SHARED_DIR)/styles/*.sty
	@echo "Compiling $< to $@"
	cd $(SLIDES_DIR) && pdflatex -interaction=nonstopmode $(notdir $<)
	cd $(SLIDES_DIR) && pdflatex -interaction=nonstopmode $(notdir $<)

[guntas-13]

@nipunbatra let me know if I should raise a PR fixing this by using the Option 3: Dependency Tracking: it works fine, now changes to shared/styles/custom.sty will allow make to track the dependency on the styles too in addition to the source .tex files
(Also will add dependency on the shared/notation/notation.sty)

$(SLIDES_DIR)/%.pdf: $(SLIDES_DIR)/%.tex $(SHARED_DIR)/styles/*.sty $(SHARED_DIR)/notation/*.sty

[nipunbatra]

Thanks @guntas-13 for noticing this!

Good catch.

I'd intended for handwritten notes to be in a separate directory as the .tex files. That way the issue would not have occurred. But, it seems that we have a lot of notes pdfs in the same directory as the .tex.

Can you please fix the paths for the notes pdfs and then hopefully this bug will be fixed.

[guntas-13]

Sure. Let me keep the notes PDFs to assets and fix the includepdf paths, and also additionally add the dependencies of shared/styles/*.sty and shared/notation/*.sty to the make so that we don't need to force clean when the style files change and make automatically sees this

[nipunbatra]

Thanks, this is reasonable. You may now go ahead and do these changes. I will pause the work on the repo for some time till tomorrow morning now.

[guntas-13]

PR #63