Two dimensional interpolation of sin(x1)exp(x2)
       x1           x2          f(x)     interpolated       error
    0.314159     0.100000     0.341517     0.340284        0.041937
    0.314159     0.300000     0.417129     0.415569        0.051215
    0.314159     0.500000     0.509483     0.507585        0.062555
    0.314159     0.700000     0.622284     0.619961        0.076405
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    0.942478     0.100000     0.894102     0.894644       -0.005991
    0.942478     0.300000     1.092059     1.092576       -0.007316
    0.942478     0.500000     1.333843     1.334496       -0.008936
    0.942478     0.700000     1.629160     1.629945       -0.010915
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    1.570796     0.100000     1.105171     1.104992        0.003595
    1.570796     0.300000     1.349859     1.349462        0.004390
    1.570796     0.500000     1.648721     1.648263        0.005362
    1.570796     0.700000     2.013753     2.013177        0.006549
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    2.199115     0.100000     0.894102     0.894644       -0.005991
    2.199115     0.300000     1.092059     1.092576       -0.007316
    2.199115     0.500000     1.333844     1.334496       -0.008936
    2.199115     0.700000     1.629160     1.629945       -0.010915
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