Parse run control block.

def _parse_run_control(block):
    """Parse run control block."""
    _, max_iterations, strain_ratio, _, _ = parse_fixed_width(
        2 * [(5, int)] + [(10, float)] + 2 * [(5, int)], block)

    return propagation.EquivalentLinearCalculation(
        strain_ratio, max_iterations, tolerance=10.)