Add option to increase `max_step` or `stop_time` to fill BTD (#3693)

* add option to increase max_step to fill BTD

* [pre-commit.ci] auto fixes from pre-commit.com hooks

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* make sure code compiles locally

* allow for unspecified max step if setting by BTD

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* clarify docs, match default max_step value

* [pre-commit.ci] auto fixes from pre-commit.com hooks

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* Apply suggestions from code review

shortening flag name

* add example input script, fix bugf

* check stop_time and max_step

* account for stop time

* Fix logic, improve documentation

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

1 files changed, 30 insertions, 7 deletions

diff --git a/Source/Diagnostics/BTDiagnostics.cpp b/Source/Diagnostics/BTDiagnostics.cpp
index 84a0501b5..ab538efb5 100644
--- a/Source/Diagnostics/BTDiagnostics.cpp
+++ b/Source/Diagnostics/BTDiagnostics.cpp
@@ -42,7 +42,7 @@
 #include <cmath>
 #include <cstdio>
 #include <memory>
-#include <string>
+#include <sstream>
 #include <vector>
 
 using namespace amrex::literals;
@@ -158,15 +158,38 @@ void BTDiagnostics::DerivedInitData ()
     // j >= i / gamma / (1+beta) * dt_snapshot / dt_boosted_frame
     const int final_snapshot_starting_step = static_cast<int>(std::ceil(final_snapshot_iteration / warpx.gamma_boost / (1._rt+warpx.beta_boost) * m_dt_snapshots_lab / dt_boosted_frame));
     const int final_snapshot_fill_iteration = final_snapshot_starting_step + num_buffers * m_buffer_size - 1;
-    if (final_snapshot_fill_iteration > warpx.maxStep()) {
-        std::string warn_string =
-            "\nSimulation might not run long enough to fill all BTD snapshots.\n"
-            "Final step: " + std::to_string(warpx.maxStep()) + "\n"
-            "Last BTD snapshot fills around step: " + std::to_string(final_snapshot_fill_iteration);
+    const amrex::Real final_snapshot_fill_time = final_snapshot_fill_iteration * dt_boosted_frame;
+    if (warpx.compute_max_step_from_btd) {
+        if (final_snapshot_fill_iteration > warpx.maxStep()) {
+            warpx.updateMaxStep(final_snapshot_fill_iteration);
+            amrex::Print()<<"max_step insufficient to fill all BTD snapshots. Automatically increased to: "
+                << final_snapshot_fill_iteration << std::endl;
+
+        }
+        if (final_snapshot_fill_time > warpx.stopTime()) {
+            warpx.updateStopTime(final_snapshot_fill_time);
+            amrex::Print()<<"stop_time insufficient to fill all BTD snapshots. Automatically increased to: "
+                << final_snapshot_fill_time << std::endl;
+
+        }
+        if (warpx.maxStep() == std::numeric_limits<int>::max() && warpx.stopTime() == std::numeric_limits<amrex::Real>::max()) {
+            amrex::Print()<<"max_step unspecified and stop time unspecified.  Setting max step to "
+                <<final_snapshot_fill_iteration<< " to fill all BTD snapshots." << std::endl;
+            warpx.updateMaxStep(final_snapshot_fill_iteration);
+        }
+
+    } else if (final_snapshot_fill_iteration > warpx.maxStep() || final_snapshot_fill_time > warpx.stopTime()) {
+        std::stringstream warn_string;
+            warn_string << "\nSimulation might not run long enough to fill all BTD snapshots.\n"
+            << "Final step: " << warpx.maxStep() << "\n"
+            <<"Stop time: " << warpx.stopTime() << "\n"
+            <<"Last BTD snapshot fills around step: " << final_snapshot_fill_iteration << "\n"
+            <<" or time: " << final_snapshot_fill_time << "\n";
         ablastr::warn_manager::WMRecordWarning(
-            "BTD", warn_string,
+            "BTD", warn_string.str(),
             ablastr::warn_manager::WarnPriority::low);
     }
+
 #ifdef WARPX_DIM_RZ
     UpdateVarnamesForRZopenPMD();
 #endif