ENH: Add link checker GitHub Action

.github/workflows/linkcheck.yml

@@ -0,0 +1,44 @@
+name: Link Checker [Anaconda, Linux]
+on:
+  pull_request:
+    types: [opened, reopened]
+  schedule:
+    # UTC 12:00 is early morning in Australia
+    - cron:  '0 12 * * *'
+jobs:
+  link-check-linux:
+    name: Link Checking (${{ matrix.python-version }}, ${{ matrix.os }})
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        os: ["ubuntu-latest"]
+        python-version: ["3.9"]
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+      - name: Setup Anaconda
+        uses: conda-incubator/setup-miniconda@v2
+        with:
+          auto-update-conda: true
+          auto-activate-base: true
+          miniconda-version: 'latest'
+          python-version: 3.9
+          environment-file: environment.yml
+          activate-environment: quantecon
+      - name: Download "build" folder (cache)
+        uses: dawidd6/action-download-artifact@v2
+        with:
+          workflow: cache.yml
+          branch: main
+          name: build-cache
+          path: _build
+      - name: Link Checker
+        shell: bash -l {0}
+        run: jb build lectures --path-output=./ --builder=custom --custom-builder=linkcheck
+      - name: Upload Link Checker Reports
+        uses: actions/upload-artifact@v2
+        if: failure()
+        with:
+          name: linkcheck-reports
+          path: _build/linkcheck

lectures/_static/quant-econ.bib

@@ -6,7 +6,6 @@
 
 @article{Orcutt_Winokur_69,
   issn      = {00129682, 14680262},
-  url       = {http://www.jstor.org/stable/1909199},
   abstract  = {Monte Carlo techniques are used to study the first order autoregressive time series model with unknown level, slope, and error variance. The effect of lagged variables on inference, estimation, and prediction is described, using results from the classical normal linear regression model as a standard. In particular, use of the t and x^2 distributions as approximate sampling distributions is verified for inference concerning the level and residual error variance. Bias in the least squares estimate of the slope is measured, and two bias corrections are evaluated. Least squares chained prediction is studied, and attempts to measure the success of prediction and to improve on the least squares technique are discussed.},
   author    = {Guy H. Orcutt and Herbert S. Winokur},
   journal   = {Econometrica},

lectures/cass_koopmans_1.md

@@ -30,7 +30,7 @@ This lecture and {doc}`Cass-Koopmans Competitive Equilibrium <cass_koopmans_2>`
 and David Cass {cite}`Cass` used to analyze optimal growth.
 
 The model can be viewed as an extension of the model of Robert Solow
-described in [an earlier lecture](https://lectures.quantecon.org/py/python_oop.html)
+described in [an earlier lecture](https://python-programming.quantecon.org/python_oop.html)
 but adapted to make the saving rate be a choice.
 
 (Solow assumed a constant saving rate determined outside the model.)

lectures/lagrangian_lqdp.md

@@ -670,7 +670,8 @@ lq.stationary_values()
 
 The preceding approach to imposing stability on a system  of potentially unstable linear difference equations is not limited to  linear quadratic dynamic optimization problems. 
 
-For example, the same method is used in our [Stability in Linear Rational Expectations Models](https://python.quantecon.org/re_with_feedback.html#Another-perspective) lecture.
+For example, the same method is used in our [Stability in Linear Rational Expectations Models](https://python.quantecon.org/re_with_feedback.html#another-perspective) lecture.
+
 
 Let's try to solve the model described in that lecture by applying the `stable_solution` function defined in this lecture above.
 

lectures/linear_algebra.md

@@ -838,7 +838,7 @@ $x$ that makes the distance $\| y - Ax\|$ as small as possible.
 To solve this problem, one can use either calculus or the theory of orthogonal
 projections.
 
-The solution is known to be $\hat x = (A'A)^{-1}A'y$ --- see for example chapter 3 of [these notes](https://lectures.quantecon.org/_downloads/course_notes.pdf).
+The solution is known to be $\hat x = (A'A)^{-1}A'y$ --- see for example chapter 3 of [these notes](https://python.quantecon.org/_static/lecture_specific/linear_algebra/course_notes.pdf).
 
 ### More Columns than Rows
 

lectures/mle.md

@@ -135,7 +135,7 @@ Let's have a look at the distribution of the data we'll be working with in this
 
 Treisman's main source of data is *Forbes'* annual rankings of billionaires and their estimated net worth.
 
-The dataset `mle/fp.dta` can be downloaded from [here](https://lectures.quantecon.org/_downloads/mle/fp.dta)
+The dataset `mle/fp.dta` can be downloaded from [here](https://python.quantecon.org/_static/lecture_specific/mle/fp.dta)
 or its [AER page](https://www.aeaweb.org/articles?id=10.1257/aer.p20161068).
 
 ```{code-cell} python3

lectures/ols.md

@@ -47,7 +47,7 @@ Along the way, we'll discuss a variety of topics, including
 
 As an example, we will replicate results from Acemoglu, Johnson and Robinson's seminal paper {cite}`Acemoglu2001`.
 
-* You can download a copy [here](https://economics.mit.edu/files/4123).
+* You can download a copy [here](http://economics.mit.edu/files/4123).
 
 In the paper, the authors emphasize the importance of institutions in economic development.
 
@@ -86,7 +86,7 @@ In this paper,
 - economic outcomes are proxied by log GDP per capita in 1995, adjusted for exchange rates.
 - institutional differences are proxied by an index of protection against expropriation on average over 1985-95, constructed by the [Political Risk Services Group](https://www.prsgroup.com/).
 
-These variables and other data used in the paper are available for download on Daron Acemoglu's [webpage](https://economics.mit.edu/faculty/acemoglu/data/ajr2001).
+These variables and other data used in the paper are available for download on Daron Acemoglu's [webpage](http://economics.mit.edu/faculty/acemoglu/data/ajr2001).
 
 We will use pandas' `.read_stata()` function to read in data contained in the `.dta` files to dataframes
 
@@ -214,7 +214,7 @@ To view the OLS regression results, we can call the `.summary()`
 method.
 
 Note that an observation was mistakenly dropped from the results in the
-original paper (see the note located in maketable2.do from Acemoglu's webpage), and thus the
+original paper (see the note located in `maketable2.do` from Acemoglu's webpage), and thus the
 coefficients differ slightly.
 
 ```{code-cell} python3

lectures/opt_transport.md

@@ -376,7 +376,7 @@ Here `'F'` stands for "Fortran", and we are using Fortran style column-major ord
 
 (For an alternative approach, using Python's default row-major ordering, see [this
         lecture by Alfred
-        Galichon](https://www.math-econ-code.org/mec-optim-b04).)
+        Galichon](https://www.math-econ-code.org/dynamic-programming).)
 
 **Interpreting the warning:**  
 

lectures/rational_expectations.md

@@ -73,7 +73,7 @@ plt.rcParams["figure.figsize"] = (11, 5)  #set default figure size
 import numpy as np
 ```
 
-We'll also use the LQ class from QuantEcon.py.
+We'll also use the LQ class from `QuantEcon.py`.
 
 ```{code-cell} ipython
 from quantecon import LQ

lectures/svd_intro.md

@@ -668,7 +668,7 @@ This
 
 Dynamic mode decomposition was introduced by {cite}`schmid2010`,
 
-You can read more about Dynamic Mode Decomposition here [[KBBWP16](https://python.quantecon.org/zreferences.html#id24)] and here [[BK19](https://python.quantecon.org/zreferences.html#id25)] (section 7.2).
+You can read more about Dynamic Mode Decomposition here {cite}`DMD_book` and here [[BK19](https://python.quantecon.org/zreferences.html#id25)] (section 7.2).
 
 
 We want to fit a **first-order vector autoregression**

lectures/wald_friedman.md

@@ -759,7 +759,7 @@ This leads to him having a higher expected loss when he puts equal weight on bot
 ### A Notebook Implementation
 
 To facilitate comparative statics, we provide
-a [Jupyter notebook](https://nbviewer.jupyter.org/github/QuantEcon/lecture-python-advanced.notebooks/blob/master/wald_friedman.ipynb) that
+a [Jupyter notebook](https://nbviewer.org/github/QuantEcon/lecture-python.notebooks/blob/master/wald_friedman.ipynb) that
 generates the same plots, but with sliders.
 
 With these sliders, you can adjust parameters and immediately observe