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-rw-r--r--libcrystfel/src/cell-utils.c33
-rw-r--r--libcrystfel/src/cell-utils.h4
2 files changed, 35 insertions, 2 deletions
diff --git a/libcrystfel/src/cell-utils.c b/libcrystfel/src/cell-utils.c
index 22610ce1..93dea212 100644
--- a/libcrystfel/src/cell-utils.c
+++ b/libcrystfel/src/cell-utils.c
@@ -3,7 +3,7 @@
*
* Unit Cell utility functions
*
- * Copyright © 2012-2020 Deutsches Elektronen-Synchrotron DESY,
+ * Copyright © 2012-2021 Deutsches Elektronen-Synchrotron DESY,
* a research centre of the Helmholtz Association.
* Copyright © 2012 Lorenzo Galli
*
@@ -1312,6 +1312,37 @@ double cell_get_volume(UnitCell *cell)
}
+/**
+ * \param cell: A %UnitCell
+ *
+ * \returns the value of 1/d for the lowest order reflection
+ * that is not systematically absent according to the centering.
+ *
+ */
+double lowest_reflection(UnitCell *cell)
+{
+ signed int h, k, l;
+ double lowres = INFINITY;
+
+ /* FIXME: Inelegant and nasty. Anyone want to work out
+ * all the possible cases? */
+ for ( h=0; h<4; h++ ) {
+ for ( k=0; k<4; k++ ) {
+ for ( l=0; l<4; l++ ) {
+ if ( (h==0) && (k==0) && (l==0) ) continue;
+ if ( !forbidden_reflection(cell, h, k, l) ) {
+ double r = resolution(cell, h, k, l);
+ if ( r < lowres ) {
+ lowres = r;
+ }
+ }
+ }
+ }
+ }
+ return lowres;
+}
+
+
/* Return true if the two centering symbols are identical,
* or if they are a pair of R/P, which should be considered the
* same for the purposes of cell comparison */
diff --git a/libcrystfel/src/cell-utils.h b/libcrystfel/src/cell-utils.h
index 00563ee6..0a110bf2 100644
--- a/libcrystfel/src/cell-utils.h
+++ b/libcrystfel/src/cell-utils.h
@@ -3,7 +3,7 @@
*
* Unit Cell utility functions
*
- * Copyright © 2012-2020 Deutsches Elektronen-Synchrotron DESY,
+ * Copyright © 2012-2021 Deutsches Elektronen-Synchrotron DESY,
* a research centre of the Helmholtz Association.
* Copyright © 2012 Lorenzo Galli
*
@@ -79,6 +79,8 @@ extern int forbidden_reflection(UnitCell *cell,
extern double cell_get_volume(UnitCell *cell);
+extern double lowest_reflection(UnitCell *cell);
+
extern int compare_cell_parameters(UnitCell *cell, UnitCell *reference,
const double *tols);