def _get_perez_coefficients(perezmodel):
    '''
    Find coefficients for the Perez model

    Parameters
    ----------

    perezmodel : string (optional, default='allsitescomposite1990')

          a character string which selects the desired set of Perez
          coefficients. If model is not provided as an input, the default,
          '1990' will be used.

    All possible model selections are:

          * '1990'
          * 'allsitescomposite1990' (same as '1990')
          * 'allsitescomposite1988'
          * 'sandiacomposite1988'
          * 'usacomposite1988'
          * 'france1988'
          * 'phoenix1988'
          * 'elmonte1988'
          * 'osage1988'
          * 'albuquerque1988'
          * 'capecanaveral1988'
          * 'albany1988'

    Returns
    --------
    F1coeffs, F2coeffs : (array, array)
          F1 and F2 coefficients for the Perez model

    References
    ----------
    [1] Loutzenhiser P.G. et. al. "Empirical validation of models to
    compute solar irradiance on inclined surfaces for building energy
    simulation" 2007, Solar Energy vol. 81. pp. 254-267

    [2] Perez, R., Seals, R., Ineichen, P., Stewart, R., Menicucci, D.,
    1987. A new simplified version of the Perez diffuse irradiance model
    for tilted surfaces. Solar Energy 39(3), 221-232.

    [3] Perez, R., Ineichen, P., Seals, R., Michalsky, J., Stewart, R.,
    1990. Modeling daylight availability and irradiance components from
    direct and global irradiance. Solar Energy 44 (5), 271-289.

    [4] Perez, R. et. al 1988. "The Development and Verification of the
    Perez Diffuse Radiation Model". SAND88-7030

    '''
    coeffdict = {
        'allsitescomposite1990': [
            [-0.0080,    0.5880,   -0.0620,   -0.0600,    0.0720,   -0.0220],
            [0.1300,    0.6830,   -0.1510,   -0.0190,    0.0660,   -0.0290],
            [0.3300,    0.4870,   -0.2210,    0.0550,   -0.0640,   -0.0260],
            [0.5680,    0.1870,   -0.2950,    0.1090,   -0.1520,   -0.0140],
            [0.8730,   -0.3920,   -0.3620,    0.2260,   -0.4620,    0.0010],
            [1.1320,   -1.2370,   -0.4120,    0.2880,   -0.8230,    0.0560],
            [1.0600,   -1.6000,   -0.3590,    0.2640,   -1.1270,    0.1310],
            [0.6780,   -0.3270,   -0.2500,    0.1560,   -1.3770,    0.2510]],
        'allsitescomposite1988': [
            [-0.0180,    0.7050,   -0.071,   -0.0580,    0.1020,   -0.0260],
            [0.1910,    0.6450,   -0.1710,    0.0120,    0.0090,   -0.0270],
            [0.4400,    0.3780,   -0.2560,    0.0870,   -0.1040,   -0.0250],
            [0.7560,   -0.1210,   -0.3460,    0.1790,   -0.3210,   -0.0080],
            [0.9960,   -0.6450,   -0.4050,    0.2600,   -0.5900,    0.0170],
            [1.0980,   -1.2900,   -0.3930,    0.2690,   -0.8320,    0.0750],
            [0.9730,   -1.1350,   -0.3780,    0.1240,   -0.2580,    0.1490],
            [0.6890,   -0.4120,   -0.2730,    0.1990,   -1.6750,    0.2370]],
        'sandiacomposite1988': [
            [-0.1960,    1.0840,   -0.0060,   -0.1140,    0.1800,   -0.0190],
            [0.2360,    0.5190,   -0.1800,   -0.0110,    0.0200,   -0.0380],
            [0.4540,    0.3210,   -0.2550,    0.0720,   -0.0980,   -0.0460],
            [0.8660,   -0.3810,   -0.3750,    0.2030,   -0.4030,   -0.0490],
            [1.0260,   -0.7110,   -0.4260,    0.2730,   -0.6020,   -0.0610],
            [0.9780,   -0.9860,   -0.3500,    0.2800,   -0.9150,   -0.0240],
            [0.7480,   -0.9130,   -0.2360,    0.1730,   -1.0450,    0.0650],
            [0.3180,   -0.7570,    0.1030,    0.0620,   -1.6980,    0.2360]],
        'usacomposite1988': [
            [-0.0340,    0.6710,   -0.0590,   -0.0590,    0.0860,   -0.0280],
            [0.2550,    0.4740,   -0.1910,    0.0180,   -0.0140,   -0.0330],
            [0.4270,    0.3490,   -0.2450,    0.0930,   -0.1210,   -0.0390],
            [0.7560,   -0.2130,   -0.3280,    0.1750,   -0.3040,   -0.0270],
            [1.0200,   -0.8570,   -0.3850,    0.2800,   -0.6380,   -0.0190],
            [1.0500,   -1.3440,   -0.3480,    0.2800,   -0.8930,    0.0370],
            [0.9740,   -1.5070,   -0.3700,    0.1540,   -0.5680,    0.1090],
            [0.7440,   -1.8170,   -0.2560,    0.2460,   -2.6180,    0.2300]],
        'france1988': [
            [0.0130,    0.7640,   -0.1000,   -0.0580,    0.1270,   -0.0230],
            [0.0950,    0.9200,   -0.1520,         0,    0.0510,   -0.0200],
            [0.4640,    0.4210,   -0.2800,    0.0640,   -0.0510,   -0.0020],
            [0.7590,   -0.0090,   -0.3730,    0.2010,   -0.3820,    0.0100],
            [0.9760,   -0.4000,   -0.4360,    0.2710,   -0.6380,    0.0510],
            [1.1760,   -1.2540,   -0.4620,    0.2950,   -0.9750,    0.1290],
            [1.1060,   -1.5630,   -0.3980,    0.3010,   -1.4420,    0.2120],
            [0.9340,   -1.5010,   -0.2710,    0.4200,   -2.9170,    0.2490]],
        'phoenix1988': [
            [-0.0030,    0.7280,   -0.0970,   -0.0750,    0.1420,   -0.0430],
            [0.2790,    0.3540,   -0.1760,    0.0300,   -0.0550,   -0.0540],
            [0.4690,    0.1680,   -0.2460,    0.0480,   -0.0420,   -0.0570],
            [0.8560,   -0.5190,   -0.3400,    0.1760,   -0.3800,   -0.0310],
            [0.9410,   -0.6250,   -0.3910,    0.1880,   -0.3600,   -0.0490],
            [1.0560,   -1.1340,   -0.4100,    0.2810,   -0.7940,   -0.0650],
            [0.9010,   -2.1390,   -0.2690,    0.1180,   -0.6650,    0.0460],
            [0.1070,    0.4810,    0.1430,   -0.1110,   -0.1370,    0.2340]],
        'elmonte1988': [
            [0.0270,    0.7010,   -0.1190,   -0.0580,    0.1070,  -0.0600],
            [0.1810,    0.6710,   -0.1780,   -0.0790,    0.1940,  -0.0350],
            [0.4760,    0.4070,   -0.2880,    0.0540,   -0.0320,  -0.0550],
            [0.8750,   -0.2180,   -0.4030,    0.1870,   -0.3090,  -0.0610],
            [1.1660,   -1.0140,   -0.4540,    0.2110,   -0.4100,  -0.0440],
            [1.1430,   -2.0640,   -0.2910,    0.0970,   -0.3190,   0.0530],
            [1.0940,   -2.6320,   -0.2590,    0.0290,   -0.4220,   0.1470],
            [0.1550,    1.7230,    0.1630,   -0.1310,   -0.0190,   0.2770]],
        'osage1988': [
            [-0.3530,    1.4740,   0.0570,   -0.1750,    0.3120,   0.0090],
            [0.3630,    0.2180,  -0.2120,    0.0190,   -0.0340,  -0.0590],
            [-0.0310,    1.2620,  -0.0840,   -0.0820,    0.2310,  -0.0170],
            [0.6910,    0.0390,  -0.2950,    0.0910,   -0.1310,  -0.0350],
            [1.1820,   -1.3500,  -0.3210,    0.4080,   -0.9850,  -0.0880],
            [0.7640,    0.0190,  -0.2030,    0.2170,   -0.2940,  -0.1030],
            [0.2190,    1.4120,   0.2440,    0.4710,   -2.9880,   0.0340],
            [3.5780,   22.2310, -10.7450,    2.4260,    4.8920,  -5.6870]],
        'albuquerque1988': [
            [0.0340,    0.5010,  -0.0940,   -0.0630,    0.1060,  -0.0440],
            [0.2290,    0.4670,  -0.1560,   -0.0050,   -0.0190,  -0.0230],
            [0.4860,    0.2410,  -0.2530,    0.0530,   -0.0640,  -0.0220],
            [0.8740,   -0.3930,  -0.3970,    0.1810,   -0.3270,  -0.0370],
            [1.1930,   -1.2960,  -0.5010,    0.2810,   -0.6560,  -0.0450],
            [1.0560,   -1.7580,  -0.3740,    0.2260,   -0.7590,   0.0340],
            [0.9010,   -4.7830,  -0.1090,    0.0630,   -0.9700,   0.1960],
            [0.8510,   -7.0550,  -0.0530,    0.0600,   -2.8330,   0.3300]],
        'capecanaveral1988': [
            [0.0750,    0.5330,   -0.1240,  -0.0670,   0.0420,  -0.0200],
            [0.2950,    0.4970,   -0.2180,  -0.0080,   0.0030,  -0.0290],
            [0.5140,    0.0810,   -0.2610,   0.0750,  -0.1600,  -0.0290],
            [0.7470,   -0.3290,   -0.3250,   0.1810,  -0.4160,  -0.0300],
            [0.9010,   -0.8830,   -0.2970,   0.1780,  -0.4890,   0.0080],
            [0.5910,   -0.0440,   -0.1160,   0.2350,  -0.9990,   0.0980],
            [0.5370,   -2.4020,    0.3200,   0.1690,  -1.9710,   0.3100],
            [-0.8050,    4.5460,    1.0720,  -0.2580,  -0.9500,    0.7530]],
        'albany1988': [
            [0.0120,    0.5540,   -0.0760, -0.0520,   0.0840,  -0.0290],
            [0.2670,    0.4370,   -0.1940,  0.0160,   0.0220,  -0.0360],
            [0.4200,    0.3360,   -0.2370,  0.0740,  -0.0520,  -0.0320],
            [0.6380,   -0.0010,   -0.2810,  0.1380,  -0.1890,  -0.0120],
            [1.0190,   -1.0270,   -0.3420,  0.2710,  -0.6280,   0.0140],
            [1.1490,   -1.9400,   -0.3310,  0.3220,  -1.0970,   0.0800],
            [1.4340,   -3.9940,   -0.4920,  0.4530,  -2.3760,   0.1170],
            [1.0070,   -2.2920,   -0.4820,  0.3900,  -3.3680,   0.2290]], }

    array = np.array(coeffdict[perezmodel])

    F1coeffs = array[:, 0:3]
    F2coeffs = array[:, 3:7]

    return F1coeffs, F2coeffs
Find coefficients for the Perez model

    Parameters
    ----------

    perezmodel : string (optional, default='allsitescomposite1990')

          a character string which selects the desired set of Perez
          coefficients. If model is not provided as an input, the default,
          '1990' will be used.

    All possible model selections are:

          * '1990'
          * 'allsitescomposite1990' (same as '1990')
          * 'allsitescomposite1988'
          * 'sandiacomposite1988'
          * 'usacomposite1988'
          * 'france1988'
          * 'phoenix1988'
          * 'elmonte1988'
          * 'osage1988'
          * 'albuquerque1988'
          * 'capecanaveral1988'
          * 'albany1988'

    Returns
    --------
    F1coeffs, F2coeffs : (array, array)
          F1 and F2 coefficients for the Perez model

    References
    ----------
    [1] Loutzenhiser P.G. et. al. "Empirical validation of models to
    compute solar irradiance on inclined surfaces for building energy
    simulation" 2007, Solar Energy vol. 81. pp. 254-267

    [2] Perez, R., Seals, R., Ineichen, P., Stewart, R., Menicucci, D.,
    1987. A new simplified version of the Perez diffuse irradiance model
    for tilted surfaces. Solar Energy 39(3), 221-232.

    [3] Perez, R., Ineichen, P., Seals, R., Michalsky, J., Stewart, R.,
    1990. Modeling daylight availability and irradiance components from
    direct and global irradiance. Solar Energy 44 (5), 271-289.

    [4] Perez, R. et. al 1988. "The Development and Verification of the
    Perez Diffuse Radiation Model". SAND88-7030