{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Spectral filtering (spectral round-trip at a lower truncation)\n",
    "\n",
    "and vizualisation of differences as (DCT) variance spectrum plot"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "execution": {
     "iopub.execute_input": "2025-01-13T11:34:00.159904Z",
     "iopub.status.busy": "2025-01-13T11:34:00.158570Z",
     "iopub.status.idle": "2025-01-13T11:34:00.688149Z",
     "shell.execute_reply": "2025-01-13T11:34:00.687560Z"
    }
   },
   "outputs": [],
   "source": [
    "%matplotlib inline\n",
    "# for figures in notebook\n",
    "\n",
    "# import & initialize epygram\n",
    "import epygram\n",
    "epygram.init_env()\n",
    "\n",
    "import os\n",
    "INPUTS_DIR = os.path.join('..', 'inputs')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "execution": {
     "iopub.execute_input": "2025-01-13T11:34:00.690407Z",
     "iopub.status.busy": "2025-01-13T11:34:00.690202Z",
     "iopub.status.idle": "2025-01-13T11:34:02.897233Z",
     "shell.execute_reply": "2025-01-13T11:34:02.896608Z"
    }
   },
   "outputs": [],
   "source": [
    "r = epygram.open(os.path.join(INPUTS_DIR, 'ICMSHAROM+0022'), 'r')\n",
    "t59 = r.readfield('S059TEMPERATURE')\n",
    "spgeom = r.spectral_geometry\n",
    "t59.sp2gp()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "execution": {
     "iopub.execute_input": "2025-01-13T11:34:02.899286Z",
     "iopub.status.busy": "2025-01-13T11:34:02.899152Z",
     "iopub.status.idle": "2025-01-13T11:34:03.086863Z",
     "shell.execute_reply": "2025-01-13T11:34:03.086358Z"
    }
   },
   "outputs": [],
   "source": [
    "# initial field spectrum\n",
    "sp59 = t59.dctspectrum()\n",
    "sp59.name = t59.fid['FA']"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "execution": {
     "iopub.execute_input": "2025-01-13T11:34:03.089076Z",
     "iopub.status.busy": "2025-01-13T11:34:03.088811Z",
     "iopub.status.idle": "2025-01-13T11:34:03.213998Z",
     "shell.execute_reply": "2025-01-13T11:34:03.213475Z"
    }
   },
   "outputs": [],
   "source": [
    "# set new spectral space\n",
    "print(spgeom.truncation['in_X'], spgeom.truncation['in_Y'])\n",
    "trunc_spgeom = spgeom.deepcopy()\n",
    "trunc_spgeom.truncation['in_X'] = 100\n",
    "trunc_spgeom.truncation['in_Y'] = 100\n",
    "# spectral roundtrip\n",
    "t59.gp2sp(trunc_spgeom)\n",
    "t59.sp2gp()\n",
    "# and compute DCT spectrum\n",
    "sp59f = t59.dctspectrum()\n",
    "sp59f.name = sp59.name + '(filtered)'"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "execution": {
     "iopub.execute_input": "2025-01-13T11:34:03.215956Z",
     "iopub.status.busy": "2025-01-13T11:34:03.215736Z",
     "iopub.status.idle": "2025-01-13T11:34:03.678853Z",
     "shell.execute_reply": "2025-01-13T11:34:03.678243Z"
    }
   },
   "outputs": [],
   "source": [
    "# and plot\n",
    "fig, ax = epygram.spectra.plotspectra([sp59, sp59f])"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  }
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