Index: /issm/trunk-jpl/externalpackages/petsc/install-3.20-mac-intel.sh
===================================================================
--- /issm/trunk-jpl/externalpackages/petsc/install-3.20-mac-intel.sh	(revision 28135)
+++ /issm/trunk-jpl/externalpackages/petsc/install-3.20-mac-intel.sh	(revision 28135)
@@ -0,0 +1,57 @@
+#!/bin/bash
+set -eu
+
+
+## Constants
+#
+VER="3.20.5"
+
+PETSC_DIR="${ISSM_DIR}/externalpackages/petsc/src" # DO NOT CHANGE THIS
+PREFIX="${ISSM_DIR}/externalpackages/petsc/install" # Set to location where external package should be installed
+
+# Download source
+$ISSM_DIR/scripts/DownloadExternalPackage.sh "https://issm.ess.uci.edu/files/externalpackages/petsc-lite-${VER}.tar.gz" "petsc-${VER}.tar.gz"
+
+# Unpack source
+tar -zxvf petsc-${VER}.tar.gz
+
+# Cleanup
+rm -rf ${PREFIX} ${PETSC_DIR}
+mkdir -p ${PETSC_DIR}
+
+# Move source to $PETSC_DIR
+mv petsc-${VER}/* ${PETSC_DIR}
+rm -rf petsc-${VER}
+
+# Apply patches
+patch src/config/BuildSystem/config/setCompilers.py < configs/3.20/mac/intel/src/config/BuildSystem/config/setCompilers.py.patch
+
+# Configure
+#
+# NOTE:
+# - Added -Wno-error=implicit-function-declaration to CFLAGS for Clang >= 12. 
+#	(may need to remove it for earlier versions not using the C99 standard).
+#
+cd ${PETSC_DIR}
+./configure \
+	--prefix="${PREFIX}" \
+	--PETSC_DIR="${PETSC_DIR}" \
+	--CFLAGS="-Wno-error=implicit-function-declaration" \
+	--LDFLAGS="-Wl,-ld_classic" \
+	--with-debugging=0 \
+	--with-valgrind=0 \
+	--with-x=0 \
+	--with-ssl=0 \
+	--with-pic=1 \
+	--download-fblaslapack=1 \
+	--download-mpich=1 \
+	--download-metis=1 \
+	--download-parmetis=1 \
+	--download-scalapack=1 \
+	--download-mumps=1 \
+	--download-zlib=1
+
+# Compile and install
+make
+make install
+