diff --git a/‎src/eval.c‎
Lines changed: 1 addition & 0 deletions b/‎src/eval.c‎
Lines changed: 1 addition & 0 deletions
diff --git a/‎src/eval.h‎
Lines changed: 1 addition & 0 deletions b/‎src/eval.h‎
Lines changed: 1 addition & 0 deletions
diff --git a/‎src/plot.c‎
Lines changed: 3 additions & 0 deletions b/‎src/plot.c‎
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@@ -56,6 +56,7 @@ static RETSIGTYPE fpe(int an_int);
 
 /* Global variables exported by this module */
 struct udvt_entry udv_pi = { NULL, "pi", {INTGR, {0} } };
+struct udvt_entry *udv_I;
 struct udvt_entry *udv_NaN;
 /* first in linked list */
 struct udvt_entry *first_udv = &udv_pi;
 
@@ -132,6 +132,7 @@ extern const struct ft_entry ft[]; /* The table of builtin functions */
 extern struct udft_entry *first_udf; /* user-def'd functions */
 extern struct udvt_entry *first_udv; /* user-def'd variables */
 extern struct udvt_entry udv_pi; /* 'pi' variable */
+extern struct udvt_entry *udv_I; /* 'I' (sqrt(-1)) */
 extern struct udvt_entry *udv_NaN; /* 'NaN' variable */
 extern struct udvt_entry **udv_user_head; /* first udv that can be deleted */
 extern TBOOLEAN undefined;
 
@@ -406,6 +406,7 @@ main(int argc_orig, char **argv)
     /* Initialize pre-loaded user variables */
     /* "pi" is hard-wired as the first variable */
     (void) add_udv_by_name("GNUTERM");
+    (void) add_udv_by_name("I");
     (void) add_udv_by_name("NaN");
     init_constants();
     udv_user_head = &(udv_NaN->next_udv);
@@ -708,6 +709,8 @@ init_constants()
     (void) Gcomplex(&udv_pi.udv_value, M_PI, 0.0);
     udv_NaN = get_udv_by_name("NaN");
     (void) Gcomplex(&(udv_NaN->udv_value), not_a_number(), 0.0);
+    udv_I = get_udv_by_name("I");
+    (void) Gcomplex(&(udv_I->udv_value), 0.0, 1.0);
 }
 
 /*